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	$100.61	12.608%	$113.2949	$113.29	$113.30	$113.30
Purchase #2	$129.35	9.653%	$141.8362	$141.84	$141.85	$141.80
Purchase #3	$128.52	11.736%	$143.6031	$143.60	$143.60	$143.60
Purchase #4	$248.93	9.502%	$272.5833	$272.58	$272.60	$272.60
Purchase #5	$88.54	13.613%	$100.593	$100.59	$100.60	$100.60
Purchase #6	$115.85	9.820%	$127.2265	$127.23	$127.25	$127.20
Purchase #7	$166.63	9.684%	$182.7664	$182.77	$182.75	$182.80
7 purchase totals =	$978.43		$1,081.9034	$1,081.90	$1,081.95	$1,081.90