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 $24.44   6.450%   $26.0164   $26.02   $26.00   $26.00  
  Purchase #2 $192.99   9.355%   $211.0442   $211.04   $211.05   $211.00  
  Purchase #3 $173.72   13.795%   $197.6847   $197.68   $197.70   $197.70  
  Purchase #4 $26.41   9.844%   $29.0098   $29.01   $29.00   $29.00  
  Purchase #5 $135.35   10.540%   $149.6159   $149.62   $149.60   $149.60  
  Purchase #6 $114.54   3.265%   $118.2797   $118.28   $118.30   $118.30  
  Purchase #7 $128.68   4.700%   $134.728   $134.73   $134.75   $134.70  
  7 purchase totals = $796.13       $866.3787   $866.38   $866.40   $866.30