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	$79.63	3.353%	$82.3	$82.30	$82.30	$82.30
Purchase #2	$196.87	7.151%	$210.9482	$210.95	$210.95	$210.90
Purchase #3	$142.43	11.354%	$158.6015	$158.60	$158.60	$158.60
Purchase #4	$93.56	11.490%	$104.31	$104.31	$104.30	$104.30
Purchase #5	$163.77	10.237%	$180.5351	$180.54	$180.55	$180.50
Purchase #6	$39.40	3.851%	$40.9173	$40.92	$40.90	$40.90
Purchase #7	$61.85	8.167%	$66.9013	$66.90	$66.90	$66.90
7 purchase totals =	$777.51		$844.5134	$844.52	$844.50	$844.40