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 $51.33   13.293%   $58.1533   $58.15   $58.15   $58.20  
  Purchase #2 $121.62   7.502%   $130.7439   $130.74   $130.75   $130.70  
  Purchase #3 $156.90   3.527%   $162.4339   $162.43   $162.45   $162.40  
  Purchase #4 $192.51   12.567%   $216.7027   $216.70   $216.70   $216.70  
  Purchase #5 $213.66   6.667%   $227.9047   $227.90   $227.90   $227.90  
  Purchase #6 $60.35   8.187%   $65.2909   $65.29   $65.30   $65.30  
  Purchase #7 $66.60   4.145%   $69.3606   $69.36   $69.35   $69.40  
  7 purchase totals = $862.97       $930.5900   $930.57   $930.60   $930.60