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 $134.41   11.471%   $149.8282   $149.83   $149.85   $149.80  
  Purchase #2 $80.82   7.105%   $86.5623   $86.56   $86.55   $86.60  
  Purchase #3 $124.65   4.524%   $130.2892   $130.29   $130.30   $130.30  
  Purchase #4 $203.77   5.487%   $214.9509   $214.95   $214.95   $215.00  
  Purchase #5 $88.84   4.637%   $92.9595   $92.96   $92.95   $93.00  
  Purchase #6 $73.29   10.717%   $81.1445   $81.14   $81.15   $81.10  
  Purchase #7 $161.33   11.122%   $179.2731   $179.27   $179.25   $179.30  
  7 purchase totals = $867.11       $935.0077   $935.00   $935.00   $935.10