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	$30.65	10.571%	$33.89	$33.89	$33.90	$33.90
Purchase #2	$147.46	12.707%	$166.1977	$166.20	$166.20	$166.20
Purchase #3	$127.72	8.396%	$138.4434	$138.44	$138.45	$138.40
Purchase #4	$56.39	9.839%	$61.9382	$61.94	$61.95	$61.90
Purchase #5	$159.60	4.322%	$166.4979	$166.50	$166.50	$166.50
Purchase #6	$55.98	5.721%	$59.1826	$59.18	$59.20	$59.20
Purchase #7	$176.52	3.865%	$183.3425	$183.34	$183.35	$183.30
7 purchase totals =	$754.32		$809.4923	$809.49	$809.55	$809.40