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 $206.68   4.360%   $215.6912   $215.69   $215.70   $215.70  
  Purchase #2 $64.31   3.489%   $66.5538   $66.55   $66.55   $66.60  
  Purchase #3 $207.57   4.799%   $217.5313   $217.53   $217.55   $217.50  
  Purchase #4 $249.71   12.477%   $280.8663   $280.87   $280.85   $280.90  
  Purchase #5 $71.63   7.805%   $77.2207   $77.22   $77.20   $77.20  
  Purchase #6 $91.88   4.690%   $96.1892   $96.19   $96.20   $96.20  
  Purchase #7 $240.76   5.113%   $253.0701   $253.07   $253.05   $253.10  
  7 purchase totals = $1,132.54       $1,207.1226   $1,207.12   $1,207.10   $1,207.20