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 $54.67   12.343%   $61.4179   $61.42   $61.40   $61.40  
  Purchase #2 $81.95   13.526%   $93.0346   $93.03   $93.05   $93.00  
  Purchase #3 $132.96   7.132%   $142.4427   $142.44   $142.45   $142.40  
  Purchase #4 $194.34   11.628%   $216.9379   $216.94   $216.95   $216.90  
  Purchase #5 $209.54   12.606%   $235.9546   $235.95   $235.95   $236.00  
  Purchase #6 $43.91   11.725%   $49.0584   $49.06   $49.05   $49.10  
  Purchase #7 $92.81   10.237%   $102.311   $102.31   $102.30   $102.30  
  7 purchase totals = $810.18       $901.1571   $901.15   $901.15   $901.10