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 $227.54   4.853%   $238.5825   $238.58   $238.60   $238.60  
  Purchase #2 $126.41   10.523%   $139.7121   $139.71   $139.70   $139.70  
  Purchase #3 $25.52   3.115%   $26.3149   $26.31   $26.30   $26.30  
  Purchase #4 $149.48   7.630%   $160.8853   $160.89   $160.90   $160.90  
  Purchase #5 $68.36   9.742%   $75.0196   $75.02   $75.00   $75.00  
  Purchase #6 $224.63   9.559%   $246.1024   $246.10   $246.10   $246.10  
  Purchase #7 $124.38   6.771%   $132.8018   $132.80   $132.80   $132.80  
  7 purchase totals = $946.32       $1,019.4186   $1,019.41   $1,019.40   $1,019.40