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 $53.87   13.652%   $61.2243   $61.22   $61.20   $61.20  
  Purchase #2 $55.77   5.155%   $58.6449   $58.64   $58.65   $58.60  
  Purchase #3 $204.98   3.508%   $212.1707   $212.17   $212.15   $212.20  
  Purchase #4 $26.98   8.118%   $29.1702   $29.17   $29.15   $29.20  
  Purchase #5 $237.74   12.768%   $268.0946   $268.09   $268.10   $268.10  
  Purchase #6 $120.58   4.677%   $126.2195   $126.22   $126.20   $126.20  
  Purchase #7 $16.83   9.452%   $18.4208   $18.42   $18.40   $18.40  
  7 purchase totals = $716.75       $773.9450   $773.93   $773.85   $773.90