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 $91.72   6.227%   $97.4314   $97.43   $97.45   $97.40  
  Purchase #2 $232.40   13.510%   $263.7972   $263.80   $263.80   $263.80  
  Purchase #3 $62.40   5.358%   $65.7434   $65.74   $65.75   $65.70  
  Purchase #4 $232.71   6.388%   $247.5755   $247.58   $247.60   $247.60  
  Purchase #5 $51.33   13.798%   $58.4125   $58.41   $58.40   $58.40  
  Purchase #6 $59.49   5.853%   $62.9719   $62.97   $62.95   $63.00  
  Purchase #7 $76.92   10.586%   $85.0628   $85.06   $85.05   $85.10  
  7 purchase totals = $806.97       $880.9947   $880.99   $881.00   $881.00