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 $59.36   6.420%   $63.1709   $63.17   $63.15   $63.20  
  Purchase #2 $104.44   7.202%   $111.9618   $111.96   $111.95   $112.00  
  Purchase #3 $168.58   13.375%   $191.1276   $191.13   $191.15   $191.10  
  Purchase #4 $55.45   12.448%   $62.3524   $62.35   $62.35   $62.40  
  Purchase #5 $159.95   9.857%   $175.7163   $175.72   $175.70   $175.70  
  Purchase #6 $112.35   12.590%   $126.4949   $126.49   $126.50   $126.50  
  Purchase #7 $62.82   12.729%   $70.8164   $70.82   $70.80   $70.80  
  7 purchase totals = $722.95       $801.6403   $801.64   $801.60   $801.70