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 $55.69   9.461%   $60.9588   $60.96   $60.95   $61.00  
  Purchase #2 $61.78   7.786%   $66.5902   $66.59   $66.60   $66.60  
  Purchase #3 $217.67   13.513%   $247.0837   $247.08   $247.10   $247.10  
  Purchase #4 $244.91   3.653%   $253.8566   $253.86   $253.85   $253.90  
  Purchase #5 $119.27   4.477%   $124.6097   $124.61   $124.60   $124.60  
  Purchase #6 $97.30   8.458%   $105.5296   $105.53   $105.55   $105.50  
  Purchase #7 $182.92   11.641%   $204.2137   $204.21   $204.20   $204.20  
  7 purchase totals = $979.54       $1,062.8423   $1,062.84   $1,062.85   $1,062.90