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 $14.29   10.313%   $15.7637   $15.76   $15.75   $15.80  
  Purchase #2 $29.90   13.366%   $33.8964   $33.90   $33.90   $33.90  
  Purchase #3 $217.78   3.504%   $225.411   $225.41   $225.40   $225.40  
  Purchase #4 $154.92   12.703%   $174.5995   $174.60   $174.60   $174.60  
  Purchase #5 $23.38   8.721%   $25.419   $25.42   $25.40   $25.40  
  Purchase #6 $119.78   9.388%   $131.0249   $131.02   $131.00   $131.00  
  Purchase #7 $191.78   5.276%   $201.8983   $201.90   $201.90   $201.90  
  7 purchase totals = $751.83       $808.0128   $808.01   $807.95   $808.00