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	$78.87	3.478%	$81.6131	$81.61	$81.60	$81.60
Purchase #2	$241.45	5.482%	$254.6863	$254.69	$254.70	$254.70
Purchase #3	$28.28	6.628%	$30.1544	$30.15	$30.15	$30.20
Purchase #4	$168.84	6.799%	$180.3194	$180.32	$180.30	$180.30
Purchase #5	$144.38	11.346%	$160.7614	$160.76	$160.75	$160.80
Purchase #6	$145.71	4.659%	$152.4986	$152.50	$152.50	$152.50
Purchase #7	$108.97	13.685%	$123.8825	$123.88	$123.90	$123.90
7 purchase totals =	$916.50		$983.9157	$983.91	$983.90	$984.00