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 $52.28   11.218%   $58.1448   $58.14   $58.15   $58.10  
  Purchase #2 $75.36   8.580%   $81.8259   $81.83   $81.85   $81.80  
  Purchase #3 $21.49   7.175%   $23.0319   $23.03   $23.05   $23.00  
  Purchase #4 $107.29   11.269%   $119.3805   $119.38   $119.40   $119.40  
  Purchase #5 $69.35   11.439%   $77.2829   $77.28   $77.30   $77.30  
  Purchase #6 $166.88   12.252%   $187.3261   $187.33   $187.35   $187.30  
  Purchase #7 $214.94   3.662%   $222.8111   $222.81   $222.80   $222.80  
  7 purchase totals = $707.59       $769.8032   $769.80   $769.90   $769.70