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 $44.76   12.193%   $50.2176   $50.22   $50.20   $50.20  
  Purchase #2 $221.79   7.132%   $237.6081   $237.61   $237.60   $237.60  
  Purchase #3 $53.94   8.578%   $58.567   $58.57   $58.55   $58.60  
  Purchase #4 $185.27   11.542%   $206.6539   $206.65   $206.65   $206.70  
  Purchase #5 $103.29   6.163%   $109.6558   $109.66   $109.65   $109.70  
  Purchase #6 $157.76   12.392%   $177.3096   $177.31   $177.30   $177.30  
  Purchase #7 $36.44   11.686%   $40.6984   $40.70   $40.70   $40.70  
  7 purchase totals = $803.25       $880.7104   $880.72   $880.65   $880.80