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	$33.84	7.119%	$36.2491	$36.25	$36.25	$36.20
Purchase #2	$166.35	8.451%	$180.4082	$180.41	$180.40	$180.40
Purchase #3	$54.89	11.394%	$61.1442	$61.14	$61.15	$61.10
Purchase #4	$46.80	7.435%	$50.2796	$50.28	$50.30	$50.30
Purchase #5	$13.74	11.653%	$15.3411	$15.34	$15.35	$15.30
Purchase #6	$74.85	4.792%	$78.4368	$78.44	$78.45	$78.40
Purchase #7	$114.49	3.690%	$118.7147	$118.71	$118.70	$118.70
7 purchase totals =	$504.96		$540.5737	$540.57	$540.60	$540.40