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	$11.41	7.274%	$12.24	$12.24	$12.25	$12.20
Purchase #2	$111.31	11.119%	$123.6866	$123.69	$123.70	$123.70
Purchase #3	$82.67	7.732%	$89.062	$89.06	$89.05	$89.10
Purchase #4	$237.80	9.491%	$260.3696	$260.37	$260.35	$260.40
Purchase #5	$98.55	13.325%	$111.6818	$111.68	$111.70	$111.70
Purchase #6	$159.82	13.736%	$181.7729	$181.77	$181.75	$181.80
Purchase #7	$162.68	5.801%	$172.1171	$172.12	$172.10	$172.10
7 purchase totals =	$864.24		$950.9300	$950.93	$950.90	$951.00