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	$146.47	6.577%	$156.1033	$156.10	$156.10	$156.10
Purchase #2	$160.89	7.156%	$172.4033	$172.40	$172.40	$172.40
Purchase #3	$182.48	12.342%	$205.0017	$205.00	$205.00	$205.00
Purchase #4	$135.53	9.292%	$148.1234	$148.12	$148.10	$148.10
Purchase #5	$68.46	6.340%	$72.8004	$72.80	$72.80	$72.80
Purchase #6	$11.58	10.462%	$12.7915	$12.79	$12.80	$12.80
Purchase #7	$78.37	3.594%	$81.1866	$81.19	$81.20	$81.20
7 purchase totals =	$783.78		$848.4102	$848.40	$848.40	$848.40