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	$13.88	12.617%	$15.6312	$15.63	$15.65	$15.60
Purchase #2	$215.57	6.564%	$229.72	$229.72	$229.70	$229.70
Purchase #3	$20.25	9.247%	$22.1225	$22.12	$22.10	$22.10
Purchase #4	$80.64	10.724%	$89.2878	$89.29	$89.30	$89.30
Purchase #5	$86.54	11.595%	$96.5743	$96.57	$96.55	$96.60
Purchase #6	$218.54	11.229%	$243.0799	$243.08	$243.10	$243.10
Purchase #7	$174.64	6.288%	$185.6214	$185.62	$185.60	$185.60
7 purchase totals =	$810.06		$882.0371	$882.03	$882.00	$882.00