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 $244.31   8.464%   $264.9884   $264.99   $265.00   $265.00  
  Purchase #2 $95.57   5.604%   $100.9257   $100.93   $100.95   $100.90  
  Purchase #3 $20.39   8.163%   $22.0544   $22.05   $22.05   $22.10  
  Purchase #4 $52.49   3.597%   $54.3781   $54.38   $54.40   $54.40  
  Purchase #5 $80.83   9.247%   $88.3044   $88.30   $88.30   $88.30  
  Purchase #6 $214.51   12.468%   $241.2551   $241.26   $241.25   $241.30  
  Purchase #7 $227.89   6.191%   $241.9987   $242.00   $242.00   $242.00  
  7 purchase totals = $935.99       $1,013.9048   $1,013.91   $1,013.95   $1,014.00