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 $222.43   11.195%   $247.331   $247.33   $247.35   $247.30  
  Purchase #2 $149.25   3.204%   $154.032   $154.03   $154.05   $154.00  
  Purchase #3 $154.37   12.368%   $173.4625   $173.46   $173.45   $173.50  
  Purchase #4 $238.98   11.549%   $266.5798   $266.58   $266.60   $266.60  
  Purchase #5 $164.35   6.841%   $175.5932   $175.59   $175.60   $175.60  
  Purchase #6 $245.33   4.232%   $255.7124   $255.71   $255.70   $255.70  
  Purchase #7 $148.90   7.207%   $159.6312   $159.63   $159.65   $159.60  
  7 purchase totals = $1,323.61       $1,432.3421   $1,432.33   $1,432.40   $1,432.30