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 $231.86   11.823%   $259.2728   $259.27   $259.25   $259.30  
  Purchase #2 $228.49   6.232%   $242.7295   $242.73   $242.75   $242.70  
  Purchase #3 $204.44   11.310%   $227.5622   $227.56   $227.55   $227.60  
  Purchase #4 $53.74   4.568%   $56.1948   $56.19   $56.20   $56.20  
  Purchase #5 $31.92   9.553%   $34.9693   $34.97   $34.95   $35.00  
  Purchase #6 $230.87   10.831%   $255.8755   $255.88   $255.90   $255.90  
  Purchase #7 $40.40   7.381%   $43.3819   $43.38   $43.40   $43.40  
  7 purchase totals = $1,021.72       $1,119.9860   $1,119.98   $1,120.00   $1,120.10