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	$27.67	3.869%	$28.7406	$28.74	$28.75	$28.70
Purchase #2	$123.35	12.693%	$139.0068	$139.01	$139.00	$139.00
Purchase #3	$123.39	3.486%	$127.6914	$127.69	$127.70	$127.70
Purchase #4	$104.30	13.340%	$118.2136	$118.21	$118.20	$118.20
Purchase #5	$99.29	10.213%	$109.4305	$109.43	$109.45	$109.40
Purchase #6	$247.55	8.250%	$267.9729	$267.97	$267.95	$268.00
Purchase #7	$86.35	4.812%	$90.5052	$90.51	$90.50	$90.50
7 purchase totals =	$811.90		$881.5610	$881.56	$881.55	$881.50