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 $231.57   9.833%   $254.3403   $254.34   $254.35   $254.30  
  Purchase #2 $199.78   3.397%   $206.5665   $206.57   $206.55   $206.60  
  Purchase #3 $215.80   11.236%   $240.0473   $240.05   $240.05   $240.00  
  Purchase #4 $215.60   12.274%   $242.0627   $242.06   $242.05   $242.10  
  Purchase #5 $57.92   6.338%   $61.591   $61.59   $61.60   $61.60  
  Purchase #6 $149.68   5.279%   $157.5816   $157.58   $157.60   $157.60  
  Purchase #7 $169.86   10.763%   $188.142   $188.14   $188.15   $188.10  
  7 purchase totals = $1,240.21       $1,350.3314   $1,350.33   $1,350.35   $1,350.30