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 $10.53   6.202%   $11.1831   $11.18   $11.20   $11.20  
  Purchase #2 $217.38   3.458%   $224.897   $224.90   $224.90   $224.90  
  Purchase #3 $61.59   10.872%   $68.2861   $68.29   $68.30   $68.30  
  Purchase #4 $223.60   4.629%   $233.9504   $233.95   $233.95   $234.00  
  Purchase #5 $223.74   11.674%   $249.8594   $249.86   $249.85   $249.90  
  Purchase #6 $179.50   5.808%   $189.9254   $189.93   $189.95   $189.90  
  Purchase #7 $154.42   5.110%   $162.3109   $162.31   $162.30   $162.30  
  7 purchase totals = $1,070.76       $1,140.4123   $1,140.42   $1,140.45   $1,140.50