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 $62.75   3.175%   $64.7423   $64.74   $64.75   $64.70  
  Purchase #2 $250.73   13.649%   $284.9521   $284.95   $284.95   $285.00  
  Purchase #3 $153.46   9.191%   $167.5645   $167.56   $167.55   $167.60  
  Purchase #4 $26.83   9.124%   $29.278   $29.28   $29.30   $29.30  
  Purchase #5 $196.92   8.560%   $213.7764   $213.78   $213.80   $213.80  
  Purchase #6 $231.43   11.867%   $258.8938   $258.89   $258.90   $258.90  
  Purchase #7 $123.80   13.605%   $140.643   $140.64   $140.65   $140.60  
  7 purchase totals = $1,045.92       $1,159.8501   $1,159.84   $1,159.90   $1,159.90