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 $57.60   8.776%   $62.655   $62.66   $62.65   $62.70  
  Purchase #2 $166.41   7.185%   $178.3666   $178.37   $178.35   $178.40  
  Purchase #3 $203.99   6.580%   $217.4125   $217.41   $217.40   $217.40  
  Purchase #4 $158.58   6.631%   $169.0954   $169.10   $169.10   $169.10  
  Purchase #5 $63.37   13.650%   $72.02   $72.02   $72.00   $72.00  
  Purchase #6 $62.96   8.374%   $68.2323   $68.23   $68.25   $68.20  
  Purchase #7 $84.40   3.205%   $87.105   $87.11   $87.10   $87.10  
  7 purchase totals = $797.31       $854.8868   $854.90   $854.85   $854.90