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	$17.39	8.748%	$18.9113	$18.91	$18.90	$18.90
Purchase #2	$97.29	8.225%	$105.2921	$105.29	$105.30	$105.30
Purchase #3	$28.54	13.677%	$32.4434	$32.44	$32.45	$32.40
Purchase #4	$155.33	3.761%	$161.172	$161.17	$161.15	$161.20
Purchase #5	$79.26	13.581%	$90.0243	$90.02	$90.00	$90.00
Purchase #6	$24.89	3.842%	$25.8463	$25.85	$25.85	$25.80
Purchase #7	$191.77	12.814%	$216.3434	$216.34	$216.35	$216.30
7 purchase totals =	$594.47		$650.0328	$650.02	$650.00	$649.90