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 $59.30   5.115%   $62.3332   $62.33   $62.35   $62.30  
  Purchase #2 $139.55   13.169%   $157.9273   $157.93   $157.95   $157.90  
  Purchase #3 $229.67   12.569%   $258.5372   $258.54   $258.55   $258.50  
  Purchase #4 $198.51   11.434%   $221.2076   $221.21   $221.20   $221.20  
  Purchase #5 $123.82   4.863%   $129.8414   $129.84   $129.85   $129.80  
  Purchase #6 $228.53   12.872%   $257.9464   $257.95   $257.95   $257.90  
  Purchase #7 $139.97   13.455%   $158.803   $158.80   $158.80   $158.80  
  7 purchase totals = $1,119.35       $1,246.5961   $1,246.60   $1,246.65   $1,246.40