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 $76.93   6.873%   $82.2174   $82.22   $82.20   $82.20  
  Purchase #2 $167.29   11.482%   $186.4982   $186.50   $186.50   $186.50  
  Purchase #3 $244.88   9.456%   $268.0359   $268.04   $268.05   $268.00  
  Purchase #4 $154.90   12.404%   $174.1138   $174.11   $174.10   $174.10  
  Purchase #5 $180.42   7.617%   $194.1626   $194.16   $194.15   $194.20  
  Purchase #6 $7.31   8.816%   $7.9544   $7.95   $7.95   $8.00  
  Purchase #7 $93.43   5.438%   $98.5107   $98.51   $98.50   $98.50  
  7 purchase totals = $925.16       $1,011.4930   $1,011.49   $1,011.45   $1,011.50