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	$52.57	13.108%	$59.4609	$59.46	$59.45	$59.50
Purchase #2	$159.77	4.247%	$166.5554	$166.56	$166.55	$166.60
Purchase #3	$39.69	13.579%	$45.0795	$45.08	$45.10	$45.10
Purchase #4	$152.99	12.327%	$171.8491	$171.85	$171.85	$171.80
Purchase #5	$175.39	13.200%	$198.5415	$198.54	$198.55	$198.50
Purchase #6	$203.84	6.364%	$216.8124	$216.81	$216.80	$216.80
Purchase #7	$236.76	8.117%	$255.9778	$255.98	$256.00	$256.00
7 purchase totals =	$1,021.01		$1,114.2766	$1,114.28	$1,114.30	$1,114.30