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	$67.74	7.851%	$73.0583	$73.06	$73.05	$73.10
Purchase #2	$179.92	4.107%	$187.3093	$187.31	$187.30	$187.30
Purchase #3	$135.72	11.420%	$151.2192	$151.22	$151.20	$151.20
Purchase #4	$90.98	9.445%	$99.5731	$99.57	$99.55	$99.60
Purchase #5	$140.42	4.344%	$146.5198	$146.52	$146.50	$146.50
Purchase #6	$127.61	12.602%	$143.6914	$143.69	$143.70	$143.70
Purchase #7	$102.40	7.839%	$110.4271	$110.43	$110.45	$110.40
7 purchase totals =	$844.79		$911.7982	$911.80	$911.75	$911.80