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 $118.70   4.153%   $123.6296   $123.63   $123.65   $123.60  
  Purchase #2 $233.74   5.198%   $245.8898   $245.89   $245.90   $245.90  
  Purchase #3 $105.42   11.186%   $117.2123   $117.21   $117.20   $117.20  
  Purchase #4 $183.28   7.809%   $197.5923   $197.59   $197.60   $197.60  
  Purchase #5 $209.71   3.765%   $217.6056   $217.61   $217.60   $217.60  
  Purchase #6 $216.40   11.779%   $241.8898   $241.89   $241.90   $241.90  
  Purchase #7 $223.45   7.207%   $239.554   $239.55   $239.55   $239.60  
  7 purchase totals = $1,290.70       $1,383.3734   $1,383.37   $1,383.40   $1,383.40