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 $82.55   13.531%   $93.7198   $93.72   $93.70   $93.70  
  Purchase #2 $210.39   3.447%   $217.6421   $217.64   $217.65   $217.60  
  Purchase #3 $54.79   11.273%   $60.9665   $60.97   $60.95   $61.00  
  Purchase #4 $63.73   8.466%   $69.1254   $69.13   $69.15   $69.10  
  Purchase #5 $200.51   9.315%   $219.1875   $219.19   $219.20   $219.20  
  Purchase #6 $109.43   13.602%   $124.3147   $124.31   $124.30   $124.30  
  Purchase #7 $250.94   5.714%   $265.2787   $265.28   $265.30   $265.30  
  7 purchase totals = $972.34       $1,050.2347   $1,050.24   $1,050.25   $1,050.20