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 $200.63   11.533%   $223.7687   $223.77   $223.75   $223.80  
  Purchase #2 $128.31   3.139%   $132.3377   $132.34   $132.35   $132.30  
  Purchase #3 $114.60   6.808%   $122.402   $122.40   $122.40   $122.40  
  Purchase #4 $70.59   3.855%   $73.3112   $73.31   $73.30   $73.30  
  Purchase #5 $108.55   6.210%   $115.291   $115.29   $115.30   $115.30  
  Purchase #6 $164.45   11.257%   $182.9621   $182.96   $182.95   $183.00  
  Purchase #7 $44.39   13.162%   $50.2326   $50.23   $50.25   $50.20  
  7 purchase totals = $831.52       $900.3053   $900.30   $900.30   $900.30