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 $153.67   13.200%   $173.9544   $173.95   $173.95   $174.00  
  Purchase #2 $94.92   9.284%   $103.7324   $103.73   $103.75   $103.70  
  Purchase #3 $62.41   6.752%   $66.6239   $66.62   $66.60   $66.60  
  Purchase #4 $238.80   8.446%   $258.969   $258.97   $258.95   $259.00  
  Purchase #5 $181.33   3.225%   $187.1779   $187.18   $187.20   $187.20  
  Purchase #6 $184.43   11.561%   $205.752   $205.75   $205.75   $205.80  
  Purchase #7 $227.61   9.571%   $249.3946   $249.39   $249.40   $249.40  
  7 purchase totals = $1,143.17       $1,245.6042   $1,245.59   $1,245.60   $1,245.70