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 $65.47   11.524%   $73.0148   $73.01   $73.00   $73.00  
  Purchase #2 $74.60   7.167%   $79.9466   $79.95   $79.95   $79.90  
  Purchase #3 $28.77   12.179%   $32.2739   $32.27   $32.25   $32.30  
  Purchase #4 $83.45   10.498%   $92.2106   $92.21   $92.20   $92.20  
  Purchase #5 $44.33   4.220%   $46.2007   $46.20   $46.20   $46.20  
  Purchase #6 $24.87   12.849%   $28.0655   $28.07   $28.05   $28.10  
  Purchase #7 $212.50   11.636%   $237.2265   $237.23   $237.25   $237.20  
  7 purchase totals = $533.99       $588.9386   $588.94   $588.90   $588.90