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 $167.85   4.271%   $175.0189   $175.02   $175.00   $175.00  
  Purchase #2 $232.26   12.533%   $261.3691   $261.37   $261.35   $261.40  
  Purchase #3 $156.86   6.713%   $167.39   $167.39   $167.40   $167.40  
  Purchase #4 $71.46   9.720%   $78.4059   $78.41   $78.40   $78.40  
  Purchase #5 $77.43   9.725%   $84.9601   $84.96   $84.95   $85.00  
  Purchase #6 $138.99   3.126%   $143.3348   $143.33   $143.35   $143.30  
  Purchase #7 $110.86   8.508%   $120.292   $120.29   $120.30   $120.30  
  7 purchase totals = $955.71       $1,030.7708   $1,030.77   $1,030.75   $1,030.80