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	$159.78	8.342%	$173.1088	$173.11	$173.10	$173.10
Purchase #2	$157.28	7.697%	$169.3858	$169.39	$169.40	$169.40
Purchase #3	$250.93	10.293%	$276.7582	$276.76	$276.75	$276.80
Purchase #4	$54.39	5.583%	$57.4266	$57.43	$57.45	$57.40
Purchase #5	$147.74	8.747%	$160.6628	$160.66	$160.65	$160.70
Purchase #6	$181.98	3.851%	$188.988	$188.99	$189.00	$189.00
Purchase #7	$52.66	13.525%	$59.7823	$59.78	$59.80	$59.80
7 purchase totals =	$1,004.76		$1,086.1125	$1,086.12	$1,086.15	$1,086.20