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 $244.27   8.589%   $265.2504   $265.25   $265.25   $265.30  
  Purchase #2 $30.42   9.192%   $33.2162   $33.22   $33.20   $33.20  
  Purchase #3 $170.69   5.813%   $180.6122   $180.61   $180.60   $180.60  
  Purchase #4 $24.50   9.363%   $26.7939   $26.79   $26.80   $26.80  
  Purchase #5 $190.49   12.680%   $214.6441   $214.64   $214.65   $214.60  
  Purchase #6 $181.48   3.674%   $188.1476   $188.15   $188.15   $188.10  
  Purchase #7 $180.31   7.531%   $193.8891   $193.89   $193.90   $193.90  
  7 purchase totals = $1,022.16       $1,102.5535   $1,102.55   $1,102.55   $1,102.50