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	$30.60	7.535%	$32.9057	$32.91	$32.90	$32.90
Purchase #2	$102.35	8.514%	$111.0641	$111.06	$111.05	$111.10
Purchase #3	$161.25	9.707%	$176.9025	$176.90	$176.90	$176.90
Purchase #4	$221.87	6.104%	$235.4129	$235.41	$235.40	$235.40
Purchase #5	$229.86	4.456%	$240.1026	$240.10	$240.10	$240.10
Purchase #6	$113.28	13.179%	$128.2092	$128.21	$128.20	$128.20
Purchase #7	$114.97	7.285%	$123.3456	$123.35	$123.35	$123.30
7 purchase totals =	$974.18		$1,047.9426	$1,047.94	$1,047.90	$1,047.90