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	$105.31	5.869%	$111.4906	$111.49	$111.50	$111.50
Purchase #2	$88.92	4.156%	$92.6155	$92.62	$92.60	$92.60
Purchase #3	$17.98	4.118%	$18.7204	$18.72	$18.70	$18.70
Purchase #4	$36.87	4.850%	$38.6582	$38.66	$38.65	$38.70
Purchase #5	$221.95	8.520%	$240.8601	$240.86	$240.85	$240.90
Purchase #6	$120.78	13.745%	$137.3812	$137.38	$137.40	$137.40
Purchase #7	$223.31	4.790%	$234.0065	$234.01	$234.00	$234.00
7 purchase totals =	$815.12		$873.7325	$873.74	$873.70	$873.80