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 $117.55   6.566%   $125.2683   $125.27   $125.25   $125.30  
  Purchase #2 $95.58   10.783%   $105.8864   $105.89   $105.90   $105.90  
  Purchase #3 $19.33   6.552%   $20.5965   $20.60   $20.60   $20.60  
  Purchase #4 $220.53   10.380%   $243.421   $243.42   $243.40   $243.40  
  Purchase #5 $207.43   4.204%   $216.1504   $216.15   $216.15   $216.20  
  Purchase #6 $169.70   10.107%   $186.8516   $186.85   $186.85   $186.90  
  Purchase #7 $46.38   3.346%   $47.9319   $47.93   $47.95   $47.90  
  7 purchase totals = $876.50       $946.1061   $946.11   $946.10   $946.20