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 $34.79   8.141%   $37.6223   $37.62   $37.60   $37.60  
  Purchase #2 $73.80   4.525%   $77.1395   $77.14   $77.15   $77.10  
  Purchase #3 $237.51   5.240%   $249.9555   $249.96   $249.95   $250.00  
  Purchase #4 $9.43   5.221%   $9.9223   $9.92   $9.90   $9.90  
  Purchase #5 $193.68   4.120%   $201.6596   $201.66   $201.65   $201.70  
  Purchase #6 $26.42   9.165%   $28.8414   $28.84   $28.85   $28.80  
  Purchase #7 $163.40   7.786%   $176.1223   $176.12   $176.10   $176.10  
  7 purchase totals = $739.03       $781.2629   $781.26   $781.20   $781.20