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	$202.36	10.286%	$223.1747	$223.17	$223.15	$223.20
Purchase #2	$181.59	5.413%	$191.4195	$191.42	$191.40	$191.40
Purchase #3	$116.43	12.689%	$131.2038	$131.20	$131.20	$131.20
Purchase #4	$25.29	13.853%	$28.7934	$28.79	$28.80	$28.80
Purchase #5	$46.85	11.328%	$52.1572	$52.16	$52.15	$52.20
Purchase #6	$57.67	9.104%	$62.9203	$62.92	$62.90	$62.90
Purchase #7	$116.65	5.795%	$123.4099	$123.41	$123.40	$123.40
7 purchase totals =	$746.84		$813.0788	$813.07	$813.00	$813.10