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	$165.47	4.285%	$172.5604	$172.56	$172.55	$172.60
Purchase #2	$90.53	6.475%	$96.3918	$96.39	$96.40	$96.40
Purchase #3	$172.87	10.411%	$190.8675	$190.87	$190.85	$190.90
Purchase #4	$139.47	13.368%	$158.1143	$158.11	$158.10	$158.10
Purchase #5	$91.73	5.205%	$96.5045	$96.50	$96.50	$96.50
Purchase #6	$53.68	7.853%	$57.8955	$57.90	$57.90	$57.90
Purchase #7	$134.63	6.238%	$143.0282	$143.03	$143.05	$143.00
7 purchase totals =	$848.38		$915.3622	$915.36	$915.35	$915.40