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 $212.82   6.329%   $226.2894   $226.29   $226.30   $226.30  
  Purchase #2 $10.39   12.485%   $11.6872   $11.69   $11.70   $11.70  
  Purchase #3 $95.37   11.548%   $106.3833   $106.38   $106.40   $106.40  
  Purchase #4 $8.88   7.669%   $9.561   $9.56   $9.55   $9.60  
  Purchase #5 $132.62   8.578%   $143.9961   $144.00   $144.00   $144.00  
  Purchase #6 $30.28   11.584%   $33.7876   $33.79   $33.80   $33.80  
  Purchase #7 $234.70   13.758%   $266.99   $266.99   $267.00   $267.00  
  7 purchase totals = $725.06       $798.6946   $798.70   $798.75   $798.80