Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $161.53   9.726%   $177.2404   $177.24   $177.25   $177.20  
  Purchase #2 $221.70   3.591%   $229.6612   $229.66   $229.65   $229.70  
  Purchase #3 $212.74   5.783%   $225.0428   $225.04   $225.05   $225.00  
  Purchase #4 $120.91   4.661%   $126.5456   $126.55   $126.55   $126.50  
  Purchase #5 $143.89   11.263%   $160.0963   $160.10   $160.10   $160.10  
  Purchase #6 $107.82   9.334%   $117.8839   $117.88   $117.90   $117.90  
  Purchase #7 $209.97   10.299%   $231.5948   $231.59   $231.60   $231.60  
  7 purchase totals = $1,178.56       $1,268.0650   $1,268.06   $1,268.10   $1,268.00