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 $55.26   12.504%   $62.1697   $62.17   $62.15   $62.20  
  Purchase #2 $235.27   13.739%   $267.5937   $267.59   $267.60   $267.60  
  Purchase #3 $159.35   7.212%   $170.8423   $170.84   $170.85   $170.80  
  Purchase #4 $31.61   12.105%   $35.4364   $35.44   $35.45   $35.40  
  Purchase #5 $143.89   3.492%   $148.9146   $148.91   $148.90   $148.90  
  Purchase #6 $86.90   5.640%   $91.8012   $91.80   $91.80   $91.80  
  Purchase #7 $216.26   10.613%   $239.2117   $239.21   $239.20   $239.20  
  7 purchase totals = $928.54       $1,015.9696   $1,015.96   $1,015.95   $1,015.90