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 $51.58   11.604%   $57.5653   $57.57   $57.55   $57.60  
  Purchase #2 $64.83   12.155%   $72.7101   $72.71   $72.70   $72.70  
  Purchase #3 $96.46   13.552%   $109.5323   $109.53   $109.55   $109.50  
  Purchase #4 $186.68   9.154%   $203.7687   $203.77   $203.75   $203.80  
  Purchase #5 $189.59   10.234%   $208.9926   $208.99   $209.00   $209.00  
  Purchase #6 $188.67   5.591%   $199.2185   $199.22   $199.20   $199.20  
  Purchase #7 $41.42   6.682%   $44.1877   $44.19   $44.20   $44.20  
  7 purchase totals = $819.23       $895.9752   $895.98   $895.95   $896.00