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	$32.94	12.326%	$37.0002	$37.00	$37.00	$37.00
Purchase #2	$10.90	12.352%	$12.2464	$12.25	$12.25	$12.20
Purchase #3	$72.33	7.364%	$77.6564	$77.66	$77.65	$77.70
Purchase #4	$184.92	12.526%	$208.0831	$208.08	$208.10	$208.10
Purchase #5	$155.51	9.470%	$170.2368	$170.24	$170.25	$170.20
Purchase #6	$89.27	12.773%	$100.6725	$100.67	$100.65	$100.70
Purchase #7	$163.77	11.658%	$182.8623	$182.86	$182.85	$182.90
7 purchase totals =	$709.64		$788.7577	$788.76	$788.75	$788.80