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 $66.86   10.348%   $73.7787   $73.78   $73.80   $73.80  
  Purchase #2 $130.69   9.371%   $142.937   $142.94   $142.95   $142.90  
  Purchase #3 $15.54   13.255%   $17.5998   $17.60   $17.60   $17.60  
  Purchase #4 $66.86   10.307%   $73.7513   $73.75   $73.75   $73.80  
  Purchase #5 $23.59   8.615%   $25.6223   $25.62   $25.60   $25.60  
  Purchase #6 $175.39   10.594%   $193.9708   $193.97   $193.95   $194.00  
  Purchase #7 $193.55   4.552%   $202.3604   $202.36   $202.35   $202.40  
  7 purchase totals = $672.48       $730.0203   $730.02   $730.00   $730.10