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	$147.45	12.782%	$166.2971	$166.30	$166.30	$166.30
Purchase #2	$230.83	8.367%	$250.1435	$250.14	$250.15	$250.10
Purchase #3	$135.59	11.747%	$151.5178	$151.52	$151.50	$151.50
Purchase #4	$38.28	6.429%	$40.741	$40.74	$40.75	$40.70
Purchase #5	$163.80	13.410%	$185.7656	$185.77	$185.75	$185.80
Purchase #6	$99.94	12.823%	$112.7553	$112.76	$112.75	$112.80
Purchase #7	$89.44	12.210%	$100.3606	$100.36	$100.35	$100.40
7 purchase totals =	$905.33		$1,007.5809	$1,007.59	$1,007.55	$1,007.60