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 $157.36   3.180%   $162.364   $162.36   $162.35   $162.40  
  Purchase #2 $9.64   13.863%   $10.9764   $10.98   $11.00   $11.00  
  Purchase #3 $57.68   3.293%   $59.5794   $59.58   $59.60   $59.60  
  Purchase #4 $96.73   12.378%   $108.7032   $108.70   $108.70   $108.70  
  Purchase #5 $183.56   8.481%   $199.1277   $199.13   $199.15   $199.10  
  Purchase #6 $226.29   9.874%   $248.6339   $248.63   $248.65   $248.60  
  Purchase #7 $95.66   3.712%   $99.2109   $99.21   $99.20   $99.20  
  7 purchase totals = $826.92       $888.5955   $888.59   $888.65   $888.60