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 $96.66   7.766%   $104.1666   $104.17   $104.15   $104.20  
  Purchase #2 $151.46   13.509%   $171.9207   $171.92   $171.90   $171.90  
  Purchase #3 $91.84   7.709%   $98.9199   $98.92   $98.90   $98.90  
  Purchase #4 $23.88   4.531%   $24.962   $24.96   $24.95   $25.00  
  Purchase #5 $242.42   3.409%   $250.6841   $250.68   $250.70   $250.70  
  Purchase #6 $129.58   13.532%   $147.1148   $147.11   $147.10   $147.10  
  Purchase #7 $57.93   6.807%   $61.8733   $61.87   $61.85   $61.90  
  7 purchase totals = $793.77       $859.6414   $859.63   $859.55   $859.70