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 $244.83   13.691%   $278.3497   $278.35   $278.35   $278.30  
  Purchase #2 $21.89   7.461%   $23.5232   $23.52   $23.50   $23.50  
  Purchase #3 $87.38   8.543%   $94.8449   $94.84   $94.85   $94.80  
  Purchase #4 $109.55   11.262%   $121.8875   $121.89   $121.90   $121.90  
  Purchase #5 $183.80   6.204%   $195.203   $195.20   $195.20   $195.20  
  Purchase #6 $214.46   10.533%   $237.0491   $237.05   $237.05   $237.00  
  Purchase #7 $78.25   5.252%   $82.3597   $82.36   $82.35   $82.40  
  7 purchase totals = $940.16       $1,033.2171   $1,033.21   $1,033.20   $1,033.10