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 $225.73   12.588%   $254.1449   $254.14   $254.15   $254.10  
  Purchase #2 $239.98   11.626%   $267.8801   $267.88   $267.90   $267.90  
  Purchase #3 $114.81   3.418%   $118.7342   $118.73   $118.75   $118.70  
  Purchase #4 $250.36   11.383%   $278.8585   $278.86   $278.85   $278.90  
  Purchase #5 $227.78   12.400%   $256.0247   $256.02   $256.00   $256.00  
  Purchase #6 $103.96   6.734%   $110.9607   $110.96   $110.95   $111.00  
  Purchase #7 $158.40   7.415%   $170.1454   $170.15   $170.15   $170.10  
  7 purchase totals = $1,321.02       $1,456.7485   $1,456.74   $1,456.75   $1,456.70