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	$65.43	13.815%	$74.4692	$74.47	$74.45	$74.50
Purchase #2	$96.45	5.297%	$101.559	$101.56	$101.55	$101.60
Purchase #3	$79.66	12.795%	$89.8525	$89.85	$89.85	$89.90
Purchase #4	$133.32	4.712%	$139.602	$139.60	$139.60	$139.60
Purchase #5	$43.90	11.472%	$48.9362	$48.94	$48.95	$48.90
Purchase #6	$205.73	6.523%	$219.1498	$219.15	$219.15	$219.10
Purchase #7	$168.55	7.304%	$180.8609	$180.86	$180.85	$180.90
7 purchase totals =	$793.04		$854.4296	$854.43	$854.40	$854.50