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	$45.62	10.796%	$50.5451	$50.55	$50.55	$50.50
Purchase #2	$166.34	6.809%	$177.6661	$177.67	$177.65	$177.70
Purchase #3	$158.52	7.180%	$169.9017	$169.90	$169.90	$169.90
Purchase #4	$114.50	11.191%	$127.3137	$127.31	$127.30	$127.30
Purchase #5	$43.79	6.335%	$46.5641	$46.56	$46.55	$46.60
Purchase #6	$109.53	6.362%	$116.4983	$116.50	$116.50	$116.50
Purchase #7	$40.87	13.746%	$46.488	$46.49	$46.50	$46.50
7 purchase totals =	$679.17		$734.9770	$734.98	$734.95	$735.00