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 $239.60   11.211%   $266.4616   $266.46   $266.45   $266.50  
  Purchase #2 $191.92   3.267%   $198.19   $198.19   $198.20   $198.20  
  Purchase #3 $44.68   3.702%   $46.3341   $46.33   $46.35   $46.30  
  Purchase #4 $33.42   4.608%   $34.96   $34.96   $34.95   $35.00  
  Purchase #5 $33.43   3.117%   $34.472   $34.47   $34.45   $34.50  
  Purchase #6 $191.95   11.620%   $214.2546   $214.25   $214.25   $214.30  
  Purchase #7 $149.94   4.558%   $156.7743   $156.77   $156.75   $156.80  
  7 purchase totals = $884.94       $951.4466   $951.43   $951.40   $951.60