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 $220.53   4.116%   $229.607   $229.61   $229.60   $229.60  
  Purchase #2 $63.53   9.677%   $69.6778   $69.68   $69.70   $69.70  
  Purchase #3 $103.73   11.446%   $115.6029   $115.60   $115.60   $115.60  
  Purchase #4 $207.70   4.581%   $217.2147   $217.21   $217.20   $217.20  
  Purchase #5 $158.77   4.568%   $166.0226   $166.02   $166.00   $166.00  
  Purchase #6 $212.36   10.566%   $234.798   $234.80   $234.80   $234.80  
  Purchase #7 $233.54   9.547%   $255.8361   $255.84   $255.85   $255.80  
  7 purchase totals = $1,200.16       $1,288.7591   $1,288.76   $1,288.75   $1,288.70