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 $202.26   7.573%   $217.5771   $217.58   $217.60   $217.60  
  Purchase #2 $82.35   3.532%   $85.2586   $85.26   $85.25   $85.30  
  Purchase #3 $234.51   4.448%   $244.941   $244.94   $244.95   $244.90  
  Purchase #4 $13.39   9.175%   $14.6185   $14.62   $14.60   $14.60  
  Purchase #5 $208.60   12.772%   $235.2424   $235.24   $235.25   $235.20  
  Purchase #6 $230.80   4.572%   $241.3522   $241.35   $241.35   $241.40  
  Purchase #7 $250.87   12.118%   $281.2704   $281.27   $281.25   $281.30  
  7 purchase totals = $1,222.78       $1,320.2602   $1,320.26   $1,320.25   $1,320.30