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 $27.32   3.117%   $28.1716   $28.17   $28.15   $28.20  
  Purchase #2 $250.74   10.191%   $276.2929   $276.29   $276.30   $276.30  
  Purchase #3 $36.67   13.854%   $41.7503   $41.75   $41.75   $41.80  
  Purchase #4 $241.68   3.526%   $250.2016   $250.20   $250.20   $250.20  
  Purchase #5 $65.70   12.108%   $73.655   $73.66   $73.65   $73.70  
  Purchase #6 $104.49   3.190%   $107.8232   $107.82   $107.80   $107.80  
  Purchase #7 $12.74   13.386%   $14.4454   $14.45   $14.45   $14.40  
  7 purchase totals = $739.34       $792.3400   $792.34   $792.30   $792.40