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 $194.82   4.278%   $203.1544   $203.15   $203.15   $203.20  
  Purchase #2 $217.55   10.762%   $240.9627   $240.96   $240.95   $241.00  
  Purchase #3 $187.31   5.355%   $197.3405   $197.34   $197.35   $197.30  
  Purchase #4 $125.50   8.138%   $135.7132   $135.71   $135.70   $135.70  
  Purchase #5 $193.36   5.223%   $203.4592   $203.46   $203.45   $203.50  
  Purchase #6 $209.50   4.133%   $218.1586   $218.16   $218.15   $218.20  
  Purchase #7 $221.27   5.848%   $234.2099   $234.21   $234.20   $234.20  
  7 purchase totals = $1,349.31       $1,432.9985   $1,432.99   $1,432.95   $1,433.10