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 $94.87   3.298%   $97.9988   $98.00   $98.00   $98.00  
  Purchase #2 $158.87   11.337%   $176.8811   $176.88   $176.90   $176.90  
  Purchase #3 $116.83   4.149%   $121.6773   $121.68   $121.70   $121.70  
  Purchase #4 $17.58   10.759%   $19.4714   $19.47   $19.45   $19.50  
  Purchase #5 $167.37   5.340%   $176.3076   $176.31   $176.30   $176.30  
  Purchase #6 $30.96   6.629%   $33.0123   $33.01   $33.00   $33.00  
  Purchase #7 $234.87   3.131%   $242.2238   $242.22   $242.20   $242.20  
  7 purchase totals = $821.35       $867.5723   $867.57   $867.55   $867.60