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 $57.29   10.696%   $63.4177   $63.42   $63.40   $63.40  
  Purchase #2 $229.88   5.523%   $242.5763   $242.58   $242.60   $242.60  
  Purchase #3 $173.55   10.681%   $192.0869   $192.09   $192.10   $192.10  
  Purchase #4 $46.93   8.471%   $50.9054   $50.91   $50.90   $50.90  
  Purchase #5 $166.93   13.805%   $189.9747   $189.97   $189.95   $190.00  
  Purchase #6 $19.72   12.357%   $22.1568   $22.16   $22.15   $22.20  
  Purchase #7 $37.46   7.290%   $40.1908   $40.19   $40.20   $40.20  
  7 purchase totals = $731.76       $801.3086   $801.32   $801.30   $801.40