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 $62.78   6.663%   $66.963   $66.96   $66.95   $67.00  
  Purchase #2 $37.56   5.306%   $39.5529   $39.55   $39.55   $39.60  
  Purchase #3 $47.94   11.162%   $53.2911   $53.29   $53.30   $53.30  
  Purchase #4 $195.61   13.561%   $222.1367   $222.14   $222.15   $222.10  
  Purchase #5 $185.67   4.296%   $193.6464   $193.65   $193.65   $193.60  
  Purchase #6 $164.86   8.486%   $178.85   $178.85   $178.85   $178.90  
  Purchase #7 $100.26   6.384%   $106.6606   $106.66   $106.65   $106.70  
  7 purchase totals = $794.68       $861.1007   $861.10   $861.10   $861.20