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	$133.37	11.107%	$148.1834	$148.18	$148.20	$148.20
Purchase #2	$212.66	6.191%	$225.8258	$225.83	$225.85	$225.80
Purchase #3	$172.77	5.293%	$181.9147	$181.91	$181.90	$181.90
Purchase #4	$119.74	3.358%	$123.7609	$123.76	$123.75	$123.80
Purchase #5	$175.51	9.554%	$192.2782	$192.28	$192.30	$192.30
Purchase #6	$38.91	11.125%	$43.2387	$43.24	$43.25	$43.20
Purchase #7	$225.82	10.711%	$250.0076	$250.01	$250.00	$250.00
7 purchase totals =	$1,078.78		$1,165.2093	$1,165.21	$1,165.25	$1,165.20