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	$75.49	12.217%	$84.7126	$84.71	$84.70	$84.70
Purchase #2	$193.64	3.658%	$200.7234	$200.72	$200.70	$200.70
Purchase #3	$117.70	10.696%	$130.2892	$130.29	$130.30	$130.30
Purchase #4	$136.54	6.212%	$145.0219	$145.02	$145.00	$145.00
Purchase #5	$106.25	5.304%	$111.8855	$111.89	$111.90	$111.90
Purchase #6	$237.69	8.607%	$258.148	$258.15	$258.15	$258.10
Purchase #7	$111.92	10.658%	$123.8484	$123.85	$123.85	$123.80
7 purchase totals =	$979.23		$1,054.6290	$1,054.63	$1,054.60	$1,054.50