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 $242.69   9.713%   $266.2625   $266.26   $266.25   $266.30  
  Purchase #2 $71.42   6.668%   $76.1823   $76.18   $76.20   $76.20  
  Purchase #3 $250.84   10.395%   $276.9148   $276.91   $276.90   $276.90  
  Purchase #4 $177.59   9.183%   $193.8981   $193.90   $193.90   $193.90  
  Purchase #5 $166.86   4.774%   $174.8259   $174.83   $174.85   $174.80  
  Purchase #6 $83.84   5.286%   $88.2718   $88.27   $88.25   $88.30  
  Purchase #7 $244.87   7.544%   $263.343   $263.34   $263.35   $263.30  
  7 purchase totals = $1,238.11       $1,339.6984   $1,339.69   $1,339.70   $1,339.70