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 $72.25   8.331%   $78.2691   $78.27   $78.25   $78.30  
  Purchase #2 $176.77   10.378%   $195.1152   $195.12   $195.10   $195.10  
  Purchase #3 $225.88   3.150%   $232.9952   $233.00   $233.00   $233.00  
  Purchase #4 $107.42   13.482%   $121.9024   $121.90   $121.90   $121.90  
  Purchase #5 $93.59   8.374%   $101.4272   $101.43   $101.45   $101.40  
  Purchase #6 $175.54   13.641%   $199.4854   $199.49   $199.50   $199.50  
  Purchase #7 $182.55   8.399%   $197.8824   $197.88   $197.90   $197.90  
  7 purchase totals = $1,034.00       $1,127.0769   $1,127.09   $1,127.10   $1,127.10