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 $57.37   9.634%   $62.897   $62.90   $62.90   $62.90  
  Purchase #2 $87.49   8.538%   $94.9599   $94.96   $94.95   $95.00  
  Purchase #3 $225.43   9.501%   $246.8481   $246.85   $246.85   $246.80  
  Purchase #4 $220.70   5.855%   $233.622   $233.62   $233.60   $233.60  
  Purchase #5 $132.37   13.299%   $149.9739   $149.97   $149.95   $150.00  
  Purchase #6 $61.91   11.489%   $69.0228   $69.02   $69.00   $69.00  
  Purchase #7 $116.94   5.180%   $122.9975   $123.00   $123.00   $123.00  
  7 purchase totals = $902.21       $980.3212   $980.32   $980.25   $980.30