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	$39.47	3.374%	$40.8017	$40.80	$40.80	$40.80
Purchase #2	$46.75	13.311%	$52.9729	$52.97	$52.95	$53.00
Purchase #3	$39.46	10.137%	$43.4601	$43.46	$43.45	$43.50
Purchase #4	$60.76	6.420%	$64.6608	$64.66	$64.65	$64.70
Purchase #5	$43.62	4.742%	$45.6885	$45.69	$45.70	$45.70
Purchase #6	$16.49	11.382%	$18.3669	$18.37	$18.35	$18.40
Purchase #7	$244.41	11.816%	$273.2895	$273.29	$273.30	$273.30
7 purchase totals =	$490.96		$539.2404	$539.24	$539.20	$539.40