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	$146.42	13.806%	$166.6347	$166.63	$166.65	$166.60
Purchase #2	$178.69	6.541%	$190.3781	$190.38	$190.40	$190.40
Purchase #3	$146.41	6.328%	$155.6748	$155.67	$155.65	$155.70
Purchase #4	$186.85	5.244%	$196.6484	$196.65	$196.65	$196.60
Purchase #5	$250.46	13.687%	$284.7405	$284.74	$284.75	$284.70
Purchase #6	$92.63	13.580%	$105.2092	$105.21	$105.20	$105.20
Purchase #7	$196.94	11.362%	$219.3163	$219.32	$219.30	$219.30
7 purchase totals =	$1,198.40		$1,318.6020	$1,318.60	$1,318.60	$1,318.50