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	$238.39	6.471%	$253.8162	$253.82	$253.80	$253.80
Purchase #2	$244.73	13.364%	$277.4357	$277.44	$277.45	$277.40
Purchase #3	$146.54	6.639%	$156.2688	$156.27	$156.25	$156.30
Purchase #4	$28.66	11.347%	$31.9121	$31.91	$31.90	$31.90
Purchase #5	$56.47	5.577%	$59.6193	$59.62	$59.60	$59.60
Purchase #6	$13.82	9.772%	$15.1705	$15.17	$15.15	$15.20
Purchase #7	$49.52	5.860%	$52.4219	$52.42	$52.40	$52.40
7 purchase totals =	$778.13		$846.6445	$846.65	$846.55	$846.60