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	$154.65	10.729%	$171.2424	$171.24	$171.25	$171.20
Purchase #2	$99.53	5.407%	$104.9116	$104.91	$104.90	$104.90
Purchase #3	$98.43	13.802%	$112.0153	$112.02	$112.00	$112.00
Purchase #4	$157.85	9.162%	$172.3122	$172.31	$172.30	$172.30
Purchase #5	$33.82	5.246%	$35.5942	$35.59	$35.60	$35.60
Purchase #6	$240.81	4.511%	$251.6729	$251.67	$251.65	$251.70
Purchase #7	$238.51	12.168%	$267.5319	$267.53	$267.55	$267.50
7 purchase totals =	$1,023.60		$1,115.2805	$1,115.27	$1,115.25	$1,115.20