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 $208.31   11.548%   $232.3656   $232.37   $232.35   $232.40  
  Purchase #2 $210.35   6.475%   $223.9702   $223.97   $223.95   $224.00  
  Purchase #3 $44.63   11.361%   $49.7004   $49.70   $49.70   $49.70  
  Purchase #4 $107.64   4.474%   $112.4558   $112.46   $112.45   $112.50  
  Purchase #5 $157.73   8.566%   $171.2412   $171.24   $171.25   $171.20  
  Purchase #6 $213.60   9.803%   $234.5392   $234.54   $234.55   $234.50  
  Purchase #7 $18.98   3.455%   $19.6358   $19.64   $19.65   $19.60  
  7 purchase totals = $961.24       $1,043.9082   $1,043.92   $1,043.90   $1,043.90