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	$233.49	7.168%	$250.2266	$250.23	$250.25	$250.20
Purchase #2	$99.56	6.230%	$105.7626	$105.76	$105.75	$105.80
Purchase #3	$150.49	13.162%	$170.2975	$170.30	$170.30	$170.30
Purchase #4	$162.52	8.619%	$176.5276	$176.53	$176.55	$176.50
Purchase #5	$113.51	5.193%	$119.4046	$119.40	$119.40	$119.40
Purchase #6	$74.46	10.446%	$82.2381	$82.24	$82.25	$82.20
Purchase #7	$40.86	7.510%	$43.9286	$43.93	$43.95	$43.90
7 purchase totals =	$874.89		$948.3856	$948.39	$948.45	$948.30