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	$38.40	13.164%	$43.455	$43.46	$43.45	$43.50
Purchase #2	$62.71	5.482%	$66.1478	$66.15	$66.15	$66.10
Purchase #3	$49.59	9.329%	$54.2163	$54.22	$54.20	$54.20
Purchase #4	$146.85	5.627%	$155.1132	$155.11	$155.10	$155.10
Purchase #5	$70.53	6.802%	$75.3275	$75.33	$75.35	$75.30
Purchase #6	$115.56	4.477%	$120.7336	$120.73	$120.75	$120.70
Purchase #7	$152.52	6.781%	$162.8624	$162.86	$162.85	$162.90
7 purchase totals =	$636.16		$677.8558	$677.86	$677.85	$677.80