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 $68.65   9.591%   $75.2342   $75.23   $75.25   $75.20  
  Purchase #2 $218.61   12.164%   $245.2017   $245.20   $245.20   $245.20  
  Purchase #3 $153.27   12.152%   $171.8954   $171.90   $171.90   $171.90  
  Purchase #4 $28.71   10.271%   $31.6588   $31.66   $31.65   $31.70  
  Purchase #5 $45.29   13.496%   $51.4023   $51.40   $51.40   $51.40  
  Purchase #6 $248.75   5.860%   $263.3268   $263.33   $263.35   $263.30  
  Purchase #7 $46.34   8.707%   $50.3748   $50.37   $50.35   $50.40  
  7 purchase totals = $809.62       $889.0940   $889.09   $889.10   $889.10