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 $101.98   12.491%   $114.7183   $114.72   $114.70   $114.70  
  Purchase #2 $223.57   10.675%   $247.4361   $247.44   $247.45   $247.40  
  Purchase #3 $10.98   4.548%   $11.4794   $11.48   $11.50   $11.50  
  Purchase #4 $20.27   11.511%   $22.6033   $22.60   $22.60   $22.60  
  Purchase #5 $217.80   12.624%   $245.2951   $245.30   $245.30   $245.30  
  Purchase #6 $123.37   5.537%   $130.201   $130.20   $130.20   $130.20  
  Purchase #7 $170.35   8.339%   $184.5555   $184.56   $184.55   $184.60  
  7 purchase totals = $868.32       $956.2887   $956.30   $956.30   $956.30