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	$240.28	13.639%	$273.0518	$273.05	$273.05	$273.10
Purchase #2	$59.35	5.782%	$62.7816	$62.78	$62.80	$62.80
Purchase #3	$74.88	4.539%	$78.2788	$78.28	$78.30	$78.30
Purchase #4	$205.28	4.364%	$214.2384	$214.24	$214.25	$214.20
Purchase #5	$57.73	7.102%	$61.83	$61.83	$61.85	$61.80
Purchase #6	$54.81	12.452%	$61.6349	$61.63	$61.65	$61.60
Purchase #7	$17.50	4.437%	$18.2765	$18.28	$18.30	$18.30
7 purchase totals =	$709.83		$770.0920	$770.09	$770.20	$770.10