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	$151.86	9.766%	$166.6906	$166.69	$166.70	$166.70
Purchase #2	$176.61	3.848%	$183.406	$183.41	$183.40	$183.40
Purchase #3	$223.28	13.377%	$253.1482	$253.15	$253.15	$253.10
Purchase #4	$212.83	11.469%	$237.2395	$237.24	$237.25	$237.20
Purchase #5	$56.43	5.279%	$59.4089	$59.41	$59.40	$59.40
Purchase #6	$51.99	3.598%	$53.8606	$53.86	$53.85	$53.90
Purchase #7	$80.95	5.304%	$85.2436	$85.24	$85.25	$85.20
7 purchase totals =	$953.95		$1,038.9974	$1,039.00	$1,039.00	$1,038.90