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 $204.26   6.631%   $217.8045   $217.80   $217.80   $217.80  
  Purchase #2 $74.30   9.343%   $81.2418   $81.24   $81.25   $81.20  
  Purchase #3 $57.84   10.597%   $63.9693   $63.97   $63.95   $64.00  
  Purchase #4 $200.93   12.559%   $226.1648   $226.16   $226.15   $226.20  
  Purchase #5 $53.25   7.815%   $57.4115   $57.41   $57.40   $57.40  
  Purchase #6 $153.38   4.335%   $160.029   $160.03   $160.05   $160.00  
  Purchase #7 $183.76   6.636%   $195.9543   $195.95   $195.95   $196.00  
  7 purchase totals = $927.72       $1,002.5752   $1,002.56   $1,002.55   $1,002.60