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 $125.57   5.307%   $132.234   $132.23   $132.25   $132.20  
  Purchase #2 $109.91   11.589%   $122.6475   $122.65   $122.65   $122.60  
  Purchase #3 $44.43   11.452%   $49.5181   $49.52   $49.50   $49.50  
  Purchase #4 $125.25   6.493%   $133.3825   $133.38   $133.40   $133.40  
  Purchase #5 $86.59   4.669%   $90.6329   $90.63   $90.65   $90.60  
  Purchase #6 $139.27   12.122%   $156.1523   $156.15   $156.15   $156.20  
  Purchase #7 $203.34   10.285%   $224.2535   $224.25   $224.25   $224.30  
  7 purchase totals = $834.36       $908.8208   $908.81   $908.85   $908.80