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 $68.51   13.568%   $77.8054   $77.81   $77.80   $77.80  
  Purchase #2 $98.48   9.513%   $107.8484   $107.85   $107.85   $107.80  
  Purchase #3 $213.28   5.442%   $224.8867   $224.89   $224.90   $224.90  
  Purchase #4 $82.41   6.676%   $87.9117   $87.91   $87.90   $87.90  
  Purchase #5 $168.58   8.322%   $182.6092   $182.61   $182.60   $182.60  
  Purchase #6 $54.65   8.597%   $59.3483   $59.35   $59.35   $59.30  
  Purchase #7 $116.33   10.356%   $128.3771   $128.38   $128.40   $128.40  
  7 purchase totals = $802.24       $868.7868   $868.80   $868.80   $868.70