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 $176.42   13.266%   $199.8239   $199.82   $199.80   $199.80  
  Purchase #2 $250.43   6.667%   $267.1262   $267.13   $267.15   $267.10  
  Purchase #3 $194.55   5.543%   $205.3339   $205.33   $205.35   $205.30  
  Purchase #4 $202.80   8.265%   $219.5614   $219.56   $219.55   $219.60  
  Purchase #5 $192.86   9.800%   $211.7603   $211.76   $211.75   $211.80  
  Purchase #6 $241.87   4.758%   $253.3782   $253.38   $253.40   $253.40  
  Purchase #7 $152.73   11.620%   $170.4772   $170.48   $170.50   $170.50  
  7 purchase totals = $1,411.66       $1,527.4611   $1,527.46   $1,527.50   $1,527.50