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	$48.82	8.342%	$52.8926	$52.89	$52.90	$52.90
Purchase #2	$57.74	12.817%	$65.1405	$65.14	$65.15	$65.10
Purchase #3	$224.62	11.348%	$250.1099	$250.11	$250.10	$250.10
Purchase #4	$136.52	10.347%	$150.6457	$150.65	$150.65	$150.60
Purchase #5	$88.60	11.834%	$99.0849	$99.08	$99.10	$99.10
Purchase #6	$49.94	12.580%	$56.2225	$56.22	$56.20	$56.20
Purchase #7	$199.25	13.279%	$225.7084	$225.71	$225.70	$225.70
7 purchase totals =	$805.49		$899.8045	$899.80	$899.80	$899.70