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	$173.27	8.224%	$187.5197	$187.52	$187.50	$187.50
Purchase #2	$40.45	10.196%	$44.5743	$44.57	$44.55	$44.60
Purchase #3	$8.35	6.862%	$8.923	$8.92	$8.90	$8.90
Purchase #4	$175.71	12.820%	$198.236	$198.24	$198.25	$198.20
Purchase #5	$148.78	4.497%	$155.4706	$155.47	$155.45	$155.50
Purchase #6	$237.48	4.456%	$248.0621	$248.06	$248.05	$248.10
Purchase #7	$78.59	8.665%	$85.3998	$85.40	$85.40	$85.40
7 purchase totals =	$862.63		$928.1855	$928.18	$928.10	$928.20