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 $230.36   13.203%   $260.7744   $260.77   $260.75   $260.80  
  Purchase #2 $244.66   13.707%   $278.1955   $278.20   $278.20   $278.20  
  Purchase #3 $180.36   11.536%   $201.1663   $201.17   $201.15   $201.20  
  Purchase #4 $58.48   6.854%   $62.4882   $62.49   $62.50   $62.50  
  Purchase #5 $243.75   6.788%   $260.2958   $260.30   $260.30   $260.30  
  Purchase #6 $56.44   5.726%   $59.6718   $59.67   $59.65   $59.70  
  Purchase #7 $223.85   4.621%   $234.1941   $234.19   $234.20   $234.20  
  7 purchase totals = $1,237.90       $1,356.7861   $1,356.79   $1,356.75   $1,356.90