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 $67.90   7.364%   $72.9002   $72.90   $72.90   $72.90  
  Purchase #2 $134.82   10.536%   $149.0246   $149.02   $149.00   $149.00  
  Purchase #3 $107.37   11.150%   $119.3418   $119.34   $119.35   $119.30  
  Purchase #4 $124.64   8.217%   $134.8817   $134.88   $134.90   $134.90  
  Purchase #5 $57.38   7.355%   $61.6003   $61.60   $61.60   $61.60  
  Purchase #6 $248.28   5.794%   $262.6653   $262.67   $262.65   $262.70  
  Purchase #7 $117.83   4.193%   $122.7706   $122.77   $122.75   $122.80  
  7 purchase totals = $858.22       $923.1845   $923.18   $923.15   $923.20