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	$53.59	7.154%	$57.4238	$57.42	$57.40	$57.40
Purchase #2	$100.82	10.244%	$111.148	$111.15	$111.15	$111.10
Purchase #3	$121.34	10.408%	$133.9691	$133.97	$133.95	$134.00
Purchase #4	$167.92	12.269%	$188.5221	$188.52	$188.50	$188.50
Purchase #5	$180.99	8.168%	$195.7733	$195.77	$195.75	$195.80
Purchase #6	$38.67	8.378%	$41.9098	$41.91	$41.90	$41.90
Purchase #7	$182.88	9.805%	$200.8114	$200.81	$200.80	$200.80
7 purchase totals =	$846.21		$929.5575	$929.55	$929.45	$929.50