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 $48.69   13.337%   $55.1838   $55.18   $55.20   $55.20  
  Purchase #2 $130.45   8.621%   $141.6961   $141.70   $141.70   $141.70  
  Purchase #3 $62.51   11.532%   $69.7187   $69.72   $69.70   $69.70  
  Purchase #4 $225.47   7.562%   $242.52   $242.52   $242.50   $242.50  
  Purchase #5 $30.96   3.659%   $32.0928   $32.09   $32.10   $32.10  
  Purchase #6 $159.98   10.394%   $176.6083   $176.61   $176.60   $176.60  
  Purchase #7 $245.75   7.141%   $263.299   $263.30   $263.30   $263.30  
  7 purchase totals = $903.81       $981.1187   $981.12   $981.10   $981.10