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 $188.65   9.204%   $206.0133   $206.01   $206.00   $206.00  
  Purchase #2 $116.91   6.238%   $124.2028   $124.20   $124.20   $124.20  
  Purchase #3 $61.83   13.771%   $70.3446   $70.34   $70.35   $70.30  
  Purchase #4 $185.94   10.665%   $205.7705   $205.77   $205.75   $205.80  
  Purchase #5 $77.48   5.515%   $81.753   $81.75   $81.75   $81.80  
  Purchase #6 $52.99   10.580%   $58.5963   $58.60   $58.60   $58.60  
  Purchase #7 $184.77   8.293%   $200.093   $200.09   $200.10   $200.10  
  7 purchase totals = $868.57       $946.7735   $946.76   $946.75   $946.80