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 $239.37   11.439%   $266.7515   $266.75   $266.75   $266.80  
  Purchase #2 $119.72   5.518%   $126.3261   $126.33   $126.35   $126.30  
  Purchase #3 $50.91   11.114%   $56.5681   $56.57   $56.55   $56.60  
  Purchase #4 $153.54   9.598%   $168.2768   $168.28   $168.30   $168.30  
  Purchase #5 $79.47   5.614%   $83.9314   $83.93   $83.95   $83.90  
  Purchase #6 $201.25   11.853%   $225.1042   $225.10   $225.10   $225.10  
  Purchase #7 $19.26   7.840%   $20.77   $20.77   $20.75   $20.80  
  7 purchase totals = $863.52       $947.7281   $947.73   $947.75   $947.80