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 $248.82   7.306%   $266.9988   $267.00   $267.00   $267.00  
  Purchase #2 $168.86   12.727%   $190.3508   $190.35   $190.35   $190.40  
  Purchase #3 $37.89   6.261%   $40.2623   $40.26   $40.25   $40.30  
  Purchase #4 $56.98   12.636%   $64.18   $64.18   $64.20   $64.20  
  Purchase #5 $75.75   13.106%   $85.6778   $85.68   $85.70   $85.70  
  Purchase #6 $49.42   12.789%   $55.7403   $55.74   $55.75   $55.70  
  Purchase #7 $72.97   10.148%   $80.375   $80.38   $80.40   $80.40  
  7 purchase totals = $710.69       $783.5850   $783.59   $783.65   $783.70