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 $94.38   10.113%   $103.9246   $103.92   $103.90   $103.90  
  Purchase #2 $95.26   13.297%   $107.9267   $107.93   $107.95   $107.90  
  Purchase #3 $47.58   12.201%   $53.3852   $53.39   $53.40   $53.40  
  Purchase #4 $85.69   9.617%   $93.9308   $93.93   $93.95   $93.90  
  Purchase #5 $227.79   8.853%   $247.9562   $247.96   $247.95   $248.00  
  Purchase #6 $115.75   12.698%   $130.4479   $130.45   $130.45   $130.40  
  Purchase #7 $37.54   10.574%   $41.5095   $41.51   $41.50   $41.50  
  7 purchase totals = $703.99       $779.0809   $779.09   $779.10   $779.00