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 $245.27   12.834%   $276.748   $276.75   $276.75   $276.70  
  Purchase #2 $205.53   13.814%   $233.9219   $233.92   $233.90   $233.90  
  Purchase #3 $60.26   5.449%   $63.5436   $63.54   $63.55   $63.50  
  Purchase #4 $152.87   5.835%   $161.79   $161.79   $161.80   $161.80  
  Purchase #5 $82.96   8.488%   $90.0016   $90.00   $90.00   $90.00  
  Purchase #6 $130.58   3.153%   $134.6972   $134.70   $134.70   $134.70  
  Purchase #7 $99.55   3.696%   $103.2294   $103.23   $103.25   $103.20  
  7 purchase totals = $977.02       $1,063.9317   $1,063.93   $1,063.95   $1,063.80