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 $60.98   6.737%   $65.0882   $65.09   $65.10   $65.10  
  Purchase #2 $236.97   8.235%   $256.4845   $256.48   $256.50   $256.50  
  Purchase #3 $179.29   8.874%   $195.2002   $195.20   $195.20   $195.20  
  Purchase #4 $92.68   9.680%   $101.6514   $101.65   $101.65   $101.70  
  Purchase #5 $95.94   7.155%   $102.8045   $102.80   $102.80   $102.80  
  Purchase #6 $217.86   4.336%   $227.3064   $227.31   $227.30   $227.30  
  Purchase #7 $121.42   3.789%   $126.0206   $126.02   $126.00   $126.00  
  7 purchase totals = $1,005.14       $1,074.5558   $1,074.55   $1,074.55   $1,074.60