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	$6.34	8.155%	$6.857	$6.86	$6.85	$6.90
Purchase #2	$186.91	6.750%	$199.5264	$199.53	$199.55	$199.50
Purchase #3	$238.73	6.661%	$254.6318	$254.63	$254.65	$254.60
Purchase #4	$66.76	6.611%	$71.1735	$71.17	$71.15	$71.20
Purchase #5	$81.58	10.765%	$90.3621	$90.36	$90.35	$90.40
Purchase #6	$115.60	6.604%	$123.2342	$123.23	$123.25	$123.20
Purchase #7	$13.34	5.516%	$14.0758	$14.08	$14.10	$14.10
7 purchase totals =	$709.26		$759.8608	$759.86	$759.90	$759.90