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	$37.89	12.205%	$42.5145	$42.51	$42.50	$42.50
Purchase #2	$75.29	13.607%	$85.5347	$85.53	$85.55	$85.50
Purchase #3	$169.87	10.450%	$187.6214	$187.62	$187.60	$187.60
Purchase #4	$181.32	11.146%	$201.5299	$201.53	$201.55	$201.50
Purchase #5	$232.41	4.801%	$243.568	$243.57	$243.55	$243.60
Purchase #6	$16.73	3.800%	$17.3657	$17.37	$17.35	$17.40
Purchase #7	$16.54	9.714%	$18.1467	$18.15	$18.15	$18.10
7 purchase totals =	$730.05		$796.2809	$796.28	$796.25	$796.20