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 $66.93   13.256%   $75.8022   $75.80   $75.80   $75.80  
  Purchase #2 $122.35   3.581%   $126.7314   $126.73   $126.75   $126.70  
  Purchase #3 $166.65   13.737%   $189.5427   $189.54   $189.55   $189.50  
  Purchase #4 $103.62   13.553%   $117.6636   $117.66   $117.65   $117.70  
  Purchase #5 $189.45   4.301%   $197.5982   $197.60   $197.60   $197.60  
  Purchase #6 $151.51   13.567%   $172.0654   $172.07   $172.05   $172.10  
  Purchase #7 $136.97   5.470%   $144.4623   $144.46   $144.45   $144.50  
  7 purchase totals = $937.48       $1,023.8658   $1,023.86   $1,023.85   $1,023.90