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 $156.96   3.403%   $162.3013   $162.30   $162.30   $162.30  
  Purchase #2 $32.82   7.339%   $35.2287   $35.23   $35.25   $35.20  
  Purchase #3 $162.92   6.543%   $173.5799   $173.58   $173.60   $173.60  
  Purchase #4 $228.73   7.293%   $245.4113   $245.41   $245.40   $245.40  
  Purchase #5 $113.52   10.307%   $125.2205   $125.22   $125.20   $125.20  
  Purchase #6 $158.55   8.846%   $172.5753   $172.58   $172.60   $172.60  
  Purchase #7 $54.55   10.370%   $60.2068   $60.21   $60.20   $60.20  
  7 purchase totals = $908.05       $974.5238   $974.53   $974.55   $974.50