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 $199.63   12.206%   $223.9968   $224.00   $224.00   $224.00  
  Purchase #2 $125.67   6.525%   $133.87   $133.87   $133.85   $133.90  
  Purchase #3 $184.84   3.622%   $191.5349   $191.53   $191.55   $191.50  
  Purchase #4 $211.58   10.828%   $234.4899   $234.49   $234.50   $234.50  
  Purchase #5 $101.60   5.345%   $107.0305   $107.03   $107.05   $107.00  
  Purchase #6 $202.31   6.484%   $215.4278   $215.43   $215.45   $215.40  
  Purchase #7 $130.26   11.246%   $144.909   $144.91   $144.90   $144.90  
  7 purchase totals = $1,155.89       $1,251.2589   $1,251.26   $1,251.30   $1,251.20