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	$47.31	6.576%	$50.4211	$50.42	$50.40	$50.40
Purchase #2	$105.30	3.852%	$109.3562	$109.36	$109.35	$109.40
Purchase #3	$48.73	9.364%	$53.2931	$53.29	$53.30	$53.30
Purchase #4	$164.72	10.849%	$182.5905	$182.59	$182.60	$182.60
Purchase #5	$85.31	7.666%	$91.8499	$91.85	$91.85	$91.80
Purchase #6	$60.78	3.509%	$62.9128	$62.91	$62.90	$62.90
Purchase #7	$72.58	10.559%	$80.2437	$80.24	$80.25	$80.20
7 purchase totals =	$584.73		$630.6673	$630.66	$630.65	$630.60