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	$40.40	13.726%	$45.9453	$45.95	$45.95	$45.90
Purchase #2	$34.61	11.851%	$38.7116	$38.71	$38.70	$38.70
Purchase #3	$53.43	5.717%	$56.4846	$56.48	$56.50	$56.50
Purchase #4	$134.39	5.739%	$142.1026	$142.10	$142.10	$142.10
Purchase #5	$36.72	9.226%	$40.1078	$40.11	$40.10	$40.10
Purchase #6	$103.88	9.621%	$113.8743	$113.87	$113.85	$113.90
Purchase #7	$105.97	7.411%	$113.8234	$113.82	$113.80	$113.80
7 purchase totals =	$509.40		$551.0496	$551.04	$551.00	$551.00