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 $236.69   13.605%   $268.8917   $268.89   $268.90   $268.90  
  Purchase #2 $224.60   4.464%   $234.6261   $234.63   $234.65   $234.60  
  Purchase #3 $77.44   9.124%   $84.5056   $84.51   $84.50   $84.50  
  Purchase #4 $95.69   5.537%   $100.9884   $100.99   $101.00   $101.00  
  Purchase #5 $115.32   9.773%   $126.5902   $126.59   $126.60   $126.60  
  Purchase #6 $247.27   8.582%   $268.4907   $268.49   $268.50   $268.50  
  Purchase #7 $58.57   5.303%   $61.676   $61.68   $61.70   $61.70  
  7 purchase totals = $1,055.58       $1,145.7687   $1,145.78   $1,145.85   $1,145.80