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	$82.65	9.764%	$90.7199	$90.72	$90.70	$90.70
Purchase #2	$130.48	9.734%	$143.1809	$143.18	$143.20	$143.20
Purchase #3	$140.99	3.154%	$145.4368	$145.44	$145.45	$145.40
Purchase #4	$70.52	5.521%	$74.4134	$74.41	$74.40	$74.40
Purchase #5	$119.96	4.684%	$125.5789	$125.58	$125.60	$125.60
Purchase #6	$40.72	7.109%	$43.6148	$43.61	$43.60	$43.60
Purchase #7	$150.53	5.190%	$158.3425	$158.34	$158.35	$158.30
7 purchase totals =	$735.85		$781.2872	$781.28	$781.30	$781.20