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 $24.55   7.528%   $26.3981   $26.40   $26.40   $26.40  
  Purchase #2 $161.94   3.636%   $167.8281   $167.83   $167.85   $167.80  
  Purchase #3 $169.83   8.288%   $183.9055   $183.91   $183.90   $183.90  
  Purchase #4 $60.63   9.455%   $66.3626   $66.36   $66.35   $66.40  
  Purchase #5 $79.55   10.477%   $87.8845   $87.88   $87.90   $87.90  
  Purchase #6 $209.43   11.147%   $232.7752   $232.78   $232.80   $232.80  
  Purchase #7 $250.37   6.516%   $266.6841   $266.68   $266.70   $266.70  
  7 purchase totals = $956.30       $1,031.8381   $1,031.84   $1,031.90   $1,031.90