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	$29.31	13.112%	$33.1531	$33.15	$33.15	$33.20
Purchase #2	$95.89	7.685%	$103.2591	$103.26	$103.25	$103.30
Purchase #3	$170.88	13.240%	$193.5045	$193.50	$193.50	$193.50
Purchase #4	$170.42	8.304%	$184.5717	$184.57	$184.55	$184.60
Purchase #5	$156.70	13.164%	$177.328	$177.33	$177.35	$177.30
Purchase #6	$116.82	5.729%	$123.5126	$123.51	$123.50	$123.50
Purchase #7	$8.94	12.540%	$10.0611	$10.06	$10.05	$10.10
7 purchase totals =	$748.96		$825.3901	$825.38	$825.35	$825.50