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	$29.82	12.841%	$33.6492	$33.65	$33.65	$33.60
Purchase #2	$104.69	6.145%	$111.1232	$111.12	$111.10	$111.10
Purchase #3	$151.92	4.190%	$158.2854	$158.29	$158.30	$158.30
Purchase #4	$58.55	10.486%	$64.6896	$64.69	$64.70	$64.70
Purchase #5	$143.88	12.743%	$162.2146	$162.21	$162.20	$162.20
Purchase #6	$55.47	10.558%	$61.3265	$61.33	$61.35	$61.30
Purchase #7	$247.89	7.864%	$267.3841	$267.38	$267.40	$267.40
7 purchase totals =	$792.22		$858.6726	$858.67	$858.70	$858.60