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 $192.61   11.408%   $214.5829   $214.58   $214.60   $214.60  
  Purchase #2 $62.39   10.259%   $68.7906   $68.79   $68.80   $68.80  
  Purchase #3 $157.99   11.656%   $176.4053   $176.41   $176.40   $176.40  
  Purchase #4 $128.47   10.858%   $142.4193   $142.42   $142.40   $142.40  
  Purchase #5 $226.31   5.708%   $239.2278   $239.23   $239.25   $239.20  
  Purchase #6 $231.96   12.228%   $260.3241   $260.32   $260.30   $260.30  
  Purchase #7 $229.28   13.273%   $259.7123   $259.71   $259.70   $259.70  
  7 purchase totals = $1,229.01       $1,361.4623   $1,361.46   $1,361.45   $1,361.40