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 $81.75   8.329%   $88.559   $88.56   $88.55   $88.60  
  Purchase #2 $38.94   4.341%   $40.6304   $40.63   $40.65   $40.60  
  Purchase #3 $42.65   7.546%   $45.8684   $45.87   $45.85   $45.90  
  Purchase #4 $88.35   11.293%   $98.3274   $98.33   $98.35   $98.30  
  Purchase #5 $205.97   9.447%   $225.428   $225.43   $225.45   $225.40  
  Purchase #6 $194.30   10.408%   $214.5227   $214.52   $214.50   $214.50  
  Purchase #7 $55.38   5.139%   $58.226   $58.23   $58.25   $58.20  
  7 purchase totals = $707.34       $771.5619   $771.57   $771.60   $771.50