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	$164.78	3.215%	$170.0777	$170.08	$170.10	$170.10
Purchase #2	$107.55	6.530%	$114.573	$114.57	$114.55	$114.60
Purchase #3	$160.96	4.579%	$168.3304	$168.33	$168.35	$168.30
Purchase #4	$154.76	11.520%	$172.5884	$172.59	$172.60	$172.60
Purchase #5	$101.94	6.810%	$108.8821	$108.88	$108.90	$108.90
Purchase #6	$6.79	13.736%	$7.7227	$7.72	$7.70	$7.70
Purchase #7	$115.77	13.346%	$131.2207	$131.22	$131.20	$131.20
7 purchase totals =	$812.55		$873.3950	$873.39	$873.40	$873.40