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 $197.98   11.791%   $221.3238   $221.32   $221.30   $221.30  
  Purchase #2 $239.55   6.408%   $254.9004   $254.90   $254.90   $254.90  
  Purchase #3 $224.75   5.802%   $237.79   $237.79   $237.80   $237.80  
  Purchase #4 $231.55   8.393%   $250.984   $250.98   $251.00   $251.00  
  Purchase #5 $67.88   13.234%   $76.8632   $76.86   $76.85   $76.90  
  Purchase #6 $174.90   11.410%   $194.8561   $194.86   $194.85   $194.90  
  Purchase #7 $47.94   4.643%   $50.1659   $50.17   $50.15   $50.20  
  7 purchase totals = $1,184.55       $1,286.8834   $1,286.88   $1,286.85   $1,287.00