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 $195.39   9.516%   $213.9833   $213.98   $214.00   $214.00  
  Purchase #2 $36.74   6.765%   $39.2255   $39.23   $39.25   $39.20  
  Purchase #3 $210.39   8.219%   $227.682   $227.68   $227.70   $227.70  
  Purchase #4 $198.85   8.742%   $216.2335   $216.23   $216.25   $216.20  
  Purchase #5 $73.41   8.808%   $79.876   $79.88   $79.90   $79.90  
  Purchase #6 $153.64   10.714%   $170.101   $170.10   $170.10   $170.10  
  Purchase #7 $19.84   8.388%   $21.5042   $21.50   $21.50   $21.50  
  7 purchase totals = $888.26       $968.6055   $968.60   $968.70   $968.60