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	$122.94	3.799%	$127.6105	$127.61	$127.60	$127.60
Purchase #2	$38.35	6.215%	$40.7335	$40.73	$40.75	$40.70
Purchase #3	$22.31	12.428%	$25.0827	$25.08	$25.10	$25.10
Purchase #4	$82.27	4.615%	$86.0668	$86.07	$86.05	$86.10
Purchase #5	$198.42	12.209%	$222.6451	$222.65	$222.65	$222.60
Purchase #6	$137.41	7.815%	$148.1486	$148.15	$148.15	$148.10
Purchase #7	$229.42	9.201%	$250.5289	$250.53	$250.55	$250.50
7 purchase totals =	$831.12		$900.8161	$900.82	$900.85	$900.70