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	$43.93	13.260%	$49.7551	$49.76	$49.75	$49.80
Purchase #2	$97.66	13.107%	$110.4603	$110.46	$110.45	$110.50
Purchase #3	$18.27	6.310%	$19.4228	$19.42	$19.40	$19.40
Purchase #4	$71.57	9.290%	$78.2189	$78.22	$78.20	$78.20
Purchase #5	$5.40	3.451%	$5.5864	$5.59	$5.60	$5.60
Purchase #6	$111.85	6.213%	$118.7992	$118.80	$118.80	$118.80
Purchase #7	$73.89	5.842%	$78.2067	$78.21	$78.20	$78.20
7 purchase totals =	$422.57		$460.4494	$460.46	$460.40	$460.50