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	$47.30	13.813%	$53.8335	$53.83	$53.85	$53.80
Purchase #2	$160.35	10.331%	$176.9158	$176.92	$176.90	$176.90
Purchase #3	$60.63	13.129%	$68.5901	$68.59	$68.60	$68.60
Purchase #4	$119.27	10.185%	$131.4176	$131.42	$131.40	$131.40
Purchase #5	$129.56	9.725%	$142.1597	$142.16	$142.15	$142.20
Purchase #6	$38.73	11.138%	$43.0437	$43.04	$43.05	$43.00
Purchase #7	$130.77	6.238%	$138.9274	$138.93	$138.95	$138.90
7 purchase totals =	$686.61		$754.8878	$754.89	$754.90	$754.80