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 $66.80   10.146%   $73.5775   $73.58   $73.60   $73.60  
  Purchase #2 $97.47   7.359%   $104.6428   $104.64   $104.65   $104.60  
  Purchase #3 $92.91   4.589%   $97.1736   $97.17   $97.15   $97.20  
  Purchase #4 $228.98   11.126%   $254.4563   $254.46   $254.45   $254.50  
  Purchase #5 $71.92   10.644%   $79.5752   $79.58   $79.60   $79.60  
  Purchase #6 $127.69   3.621%   $132.3137   $132.31   $132.30   $132.30  
  Purchase #7 $7.38   4.103%   $7.6828   $7.68   $7.70   $7.70  
  7 purchase totals = $693.15       $749.4219   $749.42   $749.45   $749.50