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 $86.77   10.778%   $96.1221   $96.12   $96.10   $96.10  
  Purchase #2 $159.27   9.198%   $173.9197   $173.92   $173.90   $173.90  
  Purchase #3 $61.64   13.117%   $69.7253   $69.73   $69.75   $69.70  
  Purchase #4 $138.78   13.422%   $157.4071   $157.41   $157.40   $157.40  
  Purchase #5 $120.57   13.357%   $136.6745   $136.67   $136.65   $136.70  
  Purchase #6 $210.63   11.323%   $234.4796   $234.48   $234.50   $234.50  
  Purchase #7 $82.35   10.235%   $90.7785   $90.78   $90.80   $90.80  
  7 purchase totals = $860.01       $959.1068   $959.11   $959.10   $959.10