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	$227.32	5.218%	$239.1816	$239.18	$239.20	$239.20
Purchase #2	$139.39	9.417%	$152.5164	$152.52	$152.50	$152.50
Purchase #3	$145.44	6.671%	$155.1423	$155.14	$155.15	$155.10
Purchase #4	$200.82	13.543%	$228.0171	$228.02	$228.00	$228.00
Purchase #5	$109.93	3.564%	$113.8479	$113.85	$113.85	$113.80
Purchase #6	$79.56	13.271%	$90.1184	$90.12	$90.10	$90.10
Purchase #7	$46.49	6.572%	$49.5453	$49.55	$49.55	$49.50
7 purchase totals =	$948.95		$1,028.3690	$1,028.38	$1,028.35	$1,028.20