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	$238.74	4.596%	$249.7125	$249.71	$249.70	$249.70
Purchase #2	$17.44	12.359%	$19.5954	$19.60	$19.60	$19.60
Purchase #3	$105.41	5.653%	$111.3688	$111.37	$111.35	$111.40
Purchase #4	$134.75	6.290%	$143.2258	$143.23	$143.25	$143.20
Purchase #5	$81.38	12.452%	$91.5134	$91.51	$91.50	$91.50
Purchase #6	$70.87	13.641%	$80.5374	$80.54	$80.55	$80.50
Purchase #7	$90.25	10.383%	$99.6207	$99.62	$99.60	$99.60
7 purchase totals =	$738.84		$795.5740	$795.58	$795.55	$795.50