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	10.402%	$172.0063	$172.01	$172.00	$172.00
Purchase #2	$30.25	10.438%	$33.4075	$33.41	$33.40	$33.40
Purchase #3	$12.31	4.676%	$12.8856	$12.89	$12.90	$12.90
Purchase #4	$139.96	10.411%	$154.5312	$154.53	$154.55	$154.50
Purchase #5	$91.94	6.798%	$98.1901	$98.19	$98.20	$98.20
Purchase #6	$190.68	10.168%	$210.0683	$210.07	$210.05	$210.10
Purchase #7	$179.37	6.397%	$190.8443	$190.84	$190.85	$190.80
7 purchase totals =	$800.31		$871.9333	$871.94	$871.95	$871.90