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	$102.57	8.199%	$110.9797	$110.98	$111.00	$111.00
Purchase #2	$141.50	4.259%	$147.5265	$147.53	$147.55	$147.50
Purchase #3	$25.69	11.849%	$28.734	$28.73	$28.75	$28.70
Purchase #4	$66.96	3.561%	$69.3444	$69.34	$69.35	$69.30
Purchase #5	$145.76	8.685%	$158.4193	$158.42	$158.40	$158.40
Purchase #6	$127.46	13.501%	$144.6684	$144.67	$144.65	$144.70
Purchase #7	$139.82	11.608%	$156.0503	$156.05	$156.05	$156.10
7 purchase totals =	$749.76		$815.7226	$815.72	$815.75	$815.70