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 $58.68   7.376%   $63.0082   $63.01   $63.00   $63.00  
  Purchase #2 $117.71   12.836%   $132.8193   $132.82   $132.80   $132.80  
  Purchase #3 $76.64   3.224%   $79.1109   $79.11   $79.10   $79.10  
  Purchase #4 $78.69   12.457%   $88.4924   $88.49   $88.50   $88.50  
  Purchase #5 $186.51   8.552%   $202.4603   $202.46   $202.45   $202.50  
  Purchase #6 $208.29   11.467%   $232.1746   $232.17   $232.15   $232.20  
  Purchase #7 $160.44   3.177%   $165.5372   $165.54   $165.55   $165.50  
  7 purchase totals = $886.96       $963.6029   $963.60   $963.55   $963.60