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 $203.29   10.503%   $224.6415   $224.64   $224.65   $224.60  
  Purchase #2 $222.90   4.857%   $233.7263   $233.73   $233.75   $233.70  
  Purchase #3 $127.52   6.787%   $136.1748   $136.17   $136.15   $136.20  
  Purchase #4 $172.65   8.591%   $187.4824   $187.48   $187.50   $187.50  
  Purchase #5 $169.50   7.609%   $182.3973   $182.40   $182.40   $182.40  
  Purchase #6 $205.51   9.452%   $224.9348   $224.93   $224.95   $224.90  
  Purchase #7 $183.83   12.109%   $206.09   $206.09   $206.10   $206.10  
  7 purchase totals = $1,285.20       $1,395.4471   $1,395.44   $1,395.50   $1,395.40