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 $174.95   11.667%   $195.3614   $195.36   $195.35   $195.40  
  Purchase #2 $117.30   12.248%   $131.6669   $131.67   $131.65   $131.70  
  Purchase #3 $66.84   6.473%   $71.1666   $71.17   $71.15   $71.20  
  Purchase #4 $241.63   7.446%   $259.6218   $259.62   $259.60   $259.60  
  Purchase #5 $122.82   11.788%   $137.298   $137.30   $137.30   $137.30  
  Purchase #6 $103.99   11.343%   $115.7856   $115.79   $115.80   $115.80  
  Purchase #7 $32.35   3.779%   $33.5725   $33.57   $33.55   $33.60  
  7 purchase totals = $859.88       $944.4728   $944.48   $944.40   $944.60