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	$73.41	9.568%	$80.4339	$80.43	$80.45	$80.40
Purchase #2	$242.76	8.713%	$263.9117	$263.91	$263.90	$263.90
Purchase #3	$165.81	11.162%	$184.3177	$184.32	$184.30	$184.30
Purchase #4	$87.57	13.238%	$99.1625	$99.16	$99.15	$99.20
Purchase #5	$219.86	4.419%	$229.5756	$229.58	$229.60	$229.60
Purchase #6	$131.49	11.766%	$146.9611	$146.96	$146.95	$147.00
Purchase #7	$86.62	5.745%	$91.5963	$91.60	$91.60	$91.60
7 purchase totals =	$1,007.52		$1,095.9588	$1,095.96	$1,095.95	$1,096.00