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 $57.76   8.369%   $62.5939   $62.59   $62.60   $62.60  
  Purchase #2 $98.36   8.119%   $106.3458   $106.35   $106.35   $106.30  
  Purchase #3 $189.85   10.540%   $209.8602   $209.86   $209.85   $209.90  
  Purchase #4 $98.63   6.834%   $105.3704   $105.37   $105.35   $105.40  
  Purchase #5 $45.61   3.335%   $47.1311   $47.13   $47.15   $47.10  
  Purchase #6 $210.31   9.169%   $229.5933   $229.59   $229.60   $229.60  
  Purchase #7 $216.27   9.386%   $236.5691   $236.57   $236.55   $236.60  
  7 purchase totals = $916.79       $997.4638   $997.46   $997.45   $997.50