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	$64.57	13.212%	$73.101	$73.10	$73.10	$73.10
Purchase #2	$50.88	6.726%	$54.3022	$54.30	$54.30	$54.30
Purchase #3	$204.72	11.372%	$228.0008	$228.00	$228.00	$228.00
Purchase #4	$168.33	10.323%	$185.7067	$185.71	$185.70	$185.70
Purchase #5	$133.72	8.686%	$145.3349	$145.33	$145.35	$145.30
Purchase #6	$71.54	4.228%	$74.5647	$74.56	$74.55	$74.60
Purchase #7	$200.57	9.456%	$219.5359	$219.54	$219.55	$219.50
7 purchase totals =	$894.33		$980.5462	$980.54	$980.55	$980.50