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	$160.55	12.215%	$180.1612	$180.16	$180.15	$180.20
Purchase #2	$23.94	4.541%	$25.0271	$25.03	$25.05	$25.00
Purchase #3	$142.59	7.207%	$152.8665	$152.87	$152.85	$152.90
Purchase #4	$212.31	6.567%	$226.2524	$226.25	$226.25	$226.30
Purchase #5	$99.95	11.459%	$111.4033	$111.40	$111.40	$111.40
Purchase #6	$63.45	13.817%	$72.2169	$72.22	$72.20	$72.20
Purchase #7	$62.67	12.313%	$70.3866	$70.39	$70.40	$70.40
7 purchase totals =	$765.46		$838.3140	$838.32	$838.30	$838.40