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	$244.52	4.808%	$256.2765	$256.28	$256.30	$256.30
Purchase #2	$224.31	11.698%	$250.5498	$250.55	$250.55	$250.50
Purchase #3	$67.69	12.719%	$76.2995	$76.30	$76.30	$76.30
Purchase #4	$127.82	5.544%	$134.9063	$134.91	$134.90	$134.90
Purchase #5	$86.36	5.108%	$90.7713	$90.77	$90.75	$90.80
Purchase #6	$141.73	6.714%	$151.2458	$151.25	$151.25	$151.20
Purchase #7	$104.67	7.477%	$112.4962	$112.50	$112.50	$112.50
7 purchase totals =	$997.10		$1,072.5454	$1,072.56	$1,072.55	$1,072.50