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 $88.46   8.795%   $96.2401   $96.24   $96.25   $96.20  
  Purchase #2 $235.71   3.614%   $244.2286   $244.23   $244.25   $244.20  
  Purchase #3 $74.40   7.392%   $79.8996   $79.90   $79.90   $79.90  
  Purchase #4 $34.61   3.854%   $35.9439   $35.94   $35.95   $35.90  
  Purchase #5 $69.97   4.504%   $73.1214   $73.12   $73.10   $73.10  
  Purchase #6 $45.32   6.469%   $48.2518   $48.25   $48.25   $48.30  
  Purchase #7 $175.51   11.821%   $196.257   $196.26   $196.25   $196.30  
  7 purchase totals = $723.98       $773.9424   $773.94   $773.95   $773.90