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 $115.34   8.761%   $125.4449   $125.44   $125.45   $125.40  
  Purchase #2 $44.31   4.563%   $46.3319   $46.33   $46.35   $46.30  
  Purchase #3 $183.59   11.690%   $205.0517   $205.05   $205.05   $205.10  
  Purchase #4 $197.38   13.363%   $223.7559   $223.76   $223.75   $223.80  
  Purchase #5 $214.95   6.579%   $229.0916   $229.09   $229.10   $229.10  
  Purchase #6 $92.69   6.290%   $98.5202   $98.52   $98.50   $98.50  
  Purchase #7 $30.39   8.615%   $33.0081   $33.01   $33.00   $33.00  
  7 purchase totals = $878.65       $961.2043   $961.20   $961.20   $961.20