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 $244.46   6.314%   $259.8952   $259.90   $259.90   $259.90  
  Purchase #2 $45.29   3.104%   $46.6958   $46.70   $46.70   $46.70  
  Purchase #3 $140.42   10.419%   $155.0504   $155.05   $155.05   $155.10  
  Purchase #4 $217.79   4.348%   $227.2595   $227.26   $227.25   $227.30  
  Purchase #5 $95.88   11.657%   $107.0567   $107.06   $107.05   $107.10  
  Purchase #6 $131.96   5.480%   $139.1914   $139.19   $139.20   $139.20  
  Purchase #7 $180.57   10.212%   $199.0098   $199.01   $199.00   $199.00  
  7 purchase totals = $1,056.37       $1,134.1588   $1,134.17   $1,134.15   $1,134.30