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 $141.63   8.720%   $153.9801   $153.98   $154.00   $154.00  
  Purchase #2 $212.38   10.801%   $235.3192   $235.32   $235.30   $235.30  
  Purchase #3 $46.42   4.798%   $48.6472   $48.65   $48.65   $48.60  
  Purchase #4 $244.64   13.276%   $277.1184   $277.12   $277.10   $277.10  
  Purchase #5 $231.46   6.686%   $246.9354   $246.94   $246.95   $246.90  
  Purchase #6 $97.51   12.301%   $109.5047   $109.50   $109.50   $109.50  
  Purchase #7 $247.47   13.320%   $280.433   $280.43   $280.45   $280.40  
  7 purchase totals = $1,221.51       $1,351.9380   $1,351.94   $1,351.95   $1,351.80