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 $98.38   3.414%   $101.7387   $101.74   $101.75   $101.70  
  Purchase #2 $44.36   4.589%   $46.3957   $46.40   $46.40   $46.40  
  Purchase #3 $153.35   6.206%   $162.8669   $162.87   $162.85   $162.90  
  Purchase #4 $64.68   11.196%   $71.9216   $71.92   $71.90   $71.90  
  Purchase #5 $219.67   13.373%   $249.0465   $249.05   $249.05   $249.00  
  Purchase #6 $108.70   9.671%   $119.2124   $119.21   $119.20   $119.20  
  Purchase #7 $113.92   4.127%   $118.6215   $118.62   $118.60   $118.60  
  7 purchase totals = $803.06       $869.8033   $869.81   $869.75   $869.70