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	$85.89	5.858%	$90.9214	$90.92	$90.90	$90.90
Purchase #2	$109.88	10.284%	$121.1801	$121.18	$121.20	$121.20
Purchase #3	$238.80	11.573%	$266.4363	$266.44	$266.45	$266.40
Purchase #4	$187.49	3.532%	$194.1121	$194.11	$194.10	$194.10
Purchase #5	$203.86	4.185%	$212.3915	$212.39	$212.40	$212.40
Purchase #6	$79.89	12.673%	$90.0145	$90.01	$90.00	$90.00
Purchase #7	$144.52	7.237%	$154.9789	$154.98	$155.00	$155.00
7 purchase totals =	$1,050.33		$1,130.0348	$1,130.03	$1,130.05	$1,130.00