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 $152.41   10.711%   $168.7346   $168.73   $168.75   $168.70  
  Purchase #2 $203.51   3.543%   $210.7204   $210.72   $210.70   $210.70  
  Purchase #3 $28.68   7.811%   $30.9202   $30.92   $30.90   $30.90  
  Purchase #4 $48.85   11.699%   $54.565   $54.57   $54.55   $54.60  
  Purchase #5 $104.81   10.565%   $115.8832   $115.88   $115.90   $115.90  
  Purchase #6 $119.40   5.381%   $125.8249   $125.82   $125.80   $125.80  
  Purchase #7 $116.52   7.361%   $125.097   $125.10   $125.10   $125.10  
  7 purchase totals = $774.18       $831.7453   $831.74   $831.70   $831.70