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 $60.83   3.147%   $62.7443   $62.74   $62.75   $62.70  
  Purchase #2 $96.37   8.842%   $104.891   $104.89   $104.90   $104.90  
  Purchase #3 $10.79   5.856%   $11.4219   $11.42   $11.40   $11.40  
  Purchase #4 $61.93   9.571%   $67.8573   $67.86   $67.85   $67.90  
  Purchase #5 $182.37   9.596%   $199.8702   $199.87   $199.85   $199.90  
  Purchase #6 $101.73   12.272%   $114.2143   $114.21   $114.20   $114.20  
  Purchase #7 $249.97   3.597%   $258.9614   $258.96   $258.95   $259.00  
  7 purchase totals = $763.99       $819.9604   $819.95   $819.90   $820.00