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	$155.80	11.363%	$173.5036	$173.50	$173.50	$173.50
Purchase #2	$60.75	11.760%	$67.8942	$67.89	$67.90	$67.90
Purchase #3	$165.30	3.440%	$170.9863	$170.99	$171.00	$171.00
Purchase #4	$38.43	11.183%	$42.7276	$42.73	$42.75	$42.70
Purchase #5	$114.86	9.170%	$125.3927	$125.39	$125.40	$125.40
Purchase #6	$75.67	13.150%	$85.6206	$85.62	$85.60	$85.60
Purchase #7	$190.65	12.857%	$215.1619	$215.16	$215.15	$215.20
7 purchase totals =	$801.46		$881.2869	$881.28	$881.30	$881.30