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 $69.43   6.114%   $73.675   $73.68   $73.70   $73.70  
  Purchase #2 $74.81   12.482%   $84.1478   $84.15   $84.15   $84.10  
  Purchase #3 $245.71   10.775%   $272.1853   $272.19   $272.20   $272.20  
  Purchase #4 $96.57   12.756%   $108.8885   $108.89   $108.90   $108.90  
  Purchase #5 $169.81   8.271%   $183.855   $183.86   $183.85   $183.90  
  Purchase #6 $130.82   3.652%   $135.5975   $135.60   $135.60   $135.60  
  Purchase #7 $84.78   8.651%   $92.1143   $92.11   $92.10   $92.10  
  7 purchase totals = $871.93       $950.4634   $950.48   $950.50   $950.50