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	$199.38	3.274%	$205.9077	$205.91	$205.90	$205.90
Purchase #2	$162.46	6.760%	$173.4423	$173.44	$173.45	$173.40
Purchase #3	$105.86	4.417%	$110.5358	$110.54	$110.55	$110.50
Purchase #4	$68.38	6.244%	$72.6496	$72.65	$72.65	$72.60
Purchase #5	$65.97	11.139%	$73.3184	$73.32	$73.30	$73.30
Purchase #6	$71.65	8.517%	$77.7524	$77.75	$77.75	$77.80
Purchase #7	$47.26	12.438%	$53.1382	$53.14	$53.15	$53.10
7 purchase totals =	$720.96		$766.7444	$766.75	$766.75	$766.60