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	$138.71	5.754%	$146.6914	$146.69	$146.70	$146.70
Purchase #2	$194.52	5.146%	$204.53	$204.53	$204.55	$204.50
Purchase #3	$53.86	5.553%	$56.8508	$56.85	$56.85	$56.90
Purchase #4	$239.91	4.257%	$250.123	$250.12	$250.10	$250.10
Purchase #5	$35.89	11.205%	$39.9115	$39.91	$39.90	$39.90
Purchase #6	$9.82	11.161%	$10.916	$10.92	$10.90	$10.90
Purchase #7	$232.66	13.498%	$264.0644	$264.06	$264.05	$264.10
7 purchase totals =	$905.37		$973.0871	$973.08	$973.05	$973.10