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 $48.86   3.648%   $50.6424   $50.64   $50.65   $50.60  
  Purchase #2 $141.78   11.599%   $158.2251   $158.23   $158.25   $158.20  
  Purchase #3 $193.37   10.204%   $213.1015   $213.10   $213.10   $213.10  
  Purchase #4 $205.52   6.126%   $218.1102   $218.11   $218.10   $218.10  
  Purchase #5 $131.46   6.818%   $140.4229   $140.42   $140.40   $140.40  
  Purchase #6 $249.91   6.103%   $265.162   $265.16   $265.15   $265.20  
  Purchase #7 $146.56   5.142%   $154.0961   $154.10   $154.10   $154.10  
  7 purchase totals = $1,117.46       $1,199.7602   $1,199.76   $1,199.75   $1,199.70