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	$37.39	5.732%	$39.5332	$39.53	$39.55	$39.50
Purchase #2	$65.97	6.514%	$70.2673	$70.27	$70.25	$70.30
Purchase #3	$89.80	10.613%	$99.3305	$99.33	$99.35	$99.30
Purchase #4	$243.81	3.469%	$252.2678	$252.27	$252.25	$252.30
Purchase #5	$232.62	10.245%	$256.4519	$256.45	$256.45	$256.50
Purchase #6	$113.61	11.532%	$126.7115	$126.71	$126.70	$126.70
Purchase #7	$40.40	13.560%	$45.8782	$45.88	$45.90	$45.90
7 purchase totals =	$823.60		$890.4404	$890.44	$890.45	$890.50