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 $91.36   12.423%   $102.7097   $102.71   $102.70   $102.70  
  Purchase #2 $106.42   12.407%   $119.6235   $119.62   $119.60   $119.60  
  Purchase #3 $36.28   8.326%   $39.3007   $39.30   $39.30   $39.30  
  Purchase #4 $109.85   4.524%   $114.8196   $114.82   $114.80   $114.80  
  Purchase #5 $248.43   3.429%   $256.9487   $256.95   $256.95   $256.90  
  Purchase #6 $138.38   5.202%   $145.5785   $145.58   $145.60   $145.60  
  Purchase #7 $234.41   4.352%   $244.6115   $244.61   $244.60   $244.60  
  7 purchase totals = $965.13       $1,023.5922   $1,023.59   $1,023.55   $1,023.50