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 $73.63   3.844%   $76.4603   $76.46   $76.45   $76.50  
  Purchase #2 $219.74   12.316%   $246.8032   $246.80   $246.80   $246.80  
  Purchase #3 $239.27   5.841%   $253.2458   $253.25   $253.25   $253.20  
  Purchase #4 $115.68   6.696%   $123.4259   $123.43   $123.45   $123.40  
  Purchase #5 $250.69   6.505%   $266.9974   $267.00   $267.00   $267.00  
  Purchase #6 $187.38   5.431%   $197.5566   $197.56   $197.55   $197.60  
  Purchase #7 $111.93   10.116%   $123.2528   $123.25   $123.25   $123.30  
  7 purchase totals = $1,198.32       $1,287.7420   $1,287.75   $1,287.75   $1,287.80