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 $184.49   11.697%   $206.0698   $206.07   $206.05   $206.10  
  Purchase #2 $57.79   4.298%   $60.2738   $60.27   $60.25   $60.30  
  Purchase #3 $166.64   11.420%   $185.6703   $185.67   $185.65   $185.70  
  Purchase #4 $162.35   8.120%   $175.5328   $175.53   $175.55   $175.50  
  Purchase #5 $7.64   3.579%   $7.9134   $7.91   $7.90   $7.90  
  Purchase #6 $71.46   12.604%   $80.4668   $80.47   $80.45   $80.50  
  Purchase #7 $48.39   11.135%   $53.7782   $53.78   $53.80   $53.80  
  7 purchase totals = $698.76       $769.7051   $769.70   $769.65   $769.80