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 $48.37   7.430%   $51.9639   $51.96   $51.95   $52.00  
  Purchase #2 $153.57   13.687%   $174.5891   $174.59   $174.60   $174.60  
  Purchase #3 $248.46   5.416%   $261.9166   $261.92   $261.90   $261.90  
  Purchase #4 $78.73   6.768%   $84.0584   $84.06   $84.05   $84.10  
  Purchase #5 $150.74   7.609%   $162.2098   $162.21   $162.20   $162.20  
  Purchase #6 $96.57   12.362%   $108.508   $108.51   $108.50   $108.50  
  Purchase #7 $109.63   3.381%   $113.3366   $113.34   $113.35   $113.30  
  7 purchase totals = $886.07       $956.5824   $956.59   $956.55   $956.60