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 $89.86   6.536%   $95.7332   $95.73   $95.75   $95.70  
  Purchase #2 $118.78   11.644%   $132.6107   $132.61   $132.60   $132.60  
  Purchase #3 $182.58   9.456%   $199.8448   $199.84   $199.85   $199.80  
  Purchase #4 $120.45   12.277%   $135.2376   $135.24   $135.25   $135.20  
  Purchase #5 $53.29   5.195%   $56.0584   $56.06   $56.05   $56.10  
  Purchase #6 $91.91   3.434%   $95.0662   $95.07   $95.05   $95.10  
  Purchase #7 $236.40   10.566%   $261.378   $261.38   $261.40   $261.40  
  7 purchase totals = $893.27       $975.9289   $975.93   $975.95   $975.90