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 $236.46   9.520%   $258.971   $258.97   $258.95   $259.00  
  Purchase #2 $38.28   4.763%   $40.1033   $40.10   $40.10   $40.10  
  Purchase #3 $33.44   4.571%   $34.9685   $34.97   $34.95   $35.00  
  Purchase #4 $237.66   8.535%   $257.9443   $257.94   $257.95   $257.90  
  Purchase #5 $183.68   8.695%   $199.651   $199.65   $199.65   $199.70  
  Purchase #6 $80.58   3.180%   $83.1424   $83.14   $83.15   $83.10  
  Purchase #7 $160.73   10.431%   $177.4957   $177.50   $177.50   $177.50  
  7 purchase totals = $970.83       $1,052.2762   $1,052.27   $1,052.25   $1,052.30