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 $168.94   9.461%   $184.9234   $184.92   $184.90   $184.90  
  Purchase #2 $90.84   11.497%   $101.2839   $101.28   $101.30   $101.30  
  Purchase #3 $82.90   5.212%   $87.2207   $87.22   $87.20   $87.20  
  Purchase #4 $245.67   12.593%   $276.6072   $276.61   $276.60   $276.60  
  Purchase #5 $179.25   12.639%   $201.9054   $201.91   $201.90   $201.90  
  Purchase #6 $103.38   11.299%   $115.0609   $115.06   $115.05   $115.10  
  Purchase #7 $73.93   7.226%   $79.2722   $79.27   $79.25   $79.30  
  7 purchase totals = $944.91       $1,046.2737   $1,046.27   $1,046.20   $1,046.30