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 $122.83   7.693%   $132.2793   $132.28   $132.30   $132.30  
  Purchase #2 $188.81   3.283%   $195.0086   $195.01   $195.00   $195.00  
  Purchase #3 $116.90   4.468%   $122.1231   $122.12   $122.10   $122.10  
  Purchase #4 $124.95   12.193%   $140.1852   $140.19   $140.20   $140.20  
  Purchase #5 $91.49   8.464%   $99.2337   $99.23   $99.25   $99.20  
  Purchase #6 $213.73   4.348%   $223.023   $223.02   $223.00   $223.00  
  Purchase #7 $55.64   8.801%   $60.5369   $60.54   $60.55   $60.50  
  7 purchase totals = $914.35       $972.3898   $972.39   $972.40   $972.30