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	$89.74	9.848%	$98.5776	$98.58	$98.60	$98.60
Purchase #2	$99.80	7.342%	$107.1273	$107.13	$107.15	$107.10
Purchase #3	$87.44	5.518%	$92.2649	$92.26	$92.25	$92.30
Purchase #4	$89.68	12.200%	$100.621	$100.62	$100.60	$100.60
Purchase #5	$25.72	10.650%	$28.4592	$28.46	$28.45	$28.50
Purchase #6	$156.32	8.306%	$169.3039	$169.30	$169.30	$169.30
Purchase #7	$101.45	11.144%	$112.7556	$112.76	$112.75	$112.80
7 purchase totals =	$650.15		$709.1095	$709.11	$709.10	$709.20