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	$28.26	4.499%	$29.5314	$29.53	$29.55	$29.50
Purchase #2	$107.31	8.841%	$116.7973	$116.80	$116.80	$116.80
Purchase #3	$149.86	10.363%	$165.39	$165.39	$165.40	$165.40
Purchase #4	$40.67	6.787%	$43.4303	$43.43	$43.45	$43.40
Purchase #5	$86.31	6.550%	$91.9633	$91.96	$91.95	$92.00
Purchase #6	$123.45	3.107%	$127.2856	$127.29	$127.30	$127.30
Purchase #7	$91.68	12.669%	$103.2949	$103.29	$103.30	$103.30
7 purchase totals =	$627.54		$677.6928	$677.69	$677.75	$677.70