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 $216.69   13.305%   $245.5206   $245.52   $245.50   $245.50  
  Purchase #2 $211.77   9.271%   $231.4032   $231.40   $231.40   $231.40  
  Purchase #3 $92.69   8.710%   $100.7633   $100.76   $100.75   $100.80  
  Purchase #4 $60.39   6.609%   $64.3812   $64.38   $64.40   $64.40  
  Purchase #5 $229.77   5.286%   $241.9156   $241.92   $241.90   $241.90  
  Purchase #6 $106.56   9.421%   $116.599   $116.60   $116.60   $116.60  
  Purchase #7 $168.67   4.601%   $176.4305   $176.43   $176.45   $176.40  
  7 purchase totals = $1,086.54       $1,177.0134   $1,177.01   $1,177.00   $1,177.00