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 $67.77   7.578%   $72.9056   $72.91   $72.90   $72.90  
  Purchase #2 $195.53   5.473%   $206.2314   $206.23   $206.25   $206.20  
  Purchase #3 $174.52   4.369%   $182.1448   $182.14   $182.15   $182.10  
  Purchase #4 $34.60   13.310%   $39.2053   $39.21   $39.20   $39.20  
  Purchase #5 $138.27   7.460%   $148.5849   $148.58   $148.60   $148.60  
  Purchase #6 $215.81   12.423%   $242.6201   $242.62   $242.60   $242.60  
  Purchase #7 $136.64   4.703%   $143.0662   $143.07   $143.05   $143.10  
  7 purchase totals = $963.14       $1,034.7583   $1,034.76   $1,034.75   $1,034.70