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	$104.35	6.617%	$111.2548	$111.25	$111.25	$111.30
Purchase #2	$181.59	12.854%	$204.9316	$204.93	$204.95	$204.90
Purchase #3	$94.65	8.278%	$102.4851	$102.49	$102.50	$102.50
Purchase #4	$46.53	10.810%	$51.5599	$51.56	$51.55	$51.60
Purchase #5	$207.99	10.821%	$230.4966	$230.50	$230.50	$230.50
Purchase #6	$245.71	7.687%	$264.5977	$264.60	$264.60	$264.60
Purchase #7	$39.79	10.132%	$43.8215	$43.82	$43.80	$43.80
7 purchase totals =	$920.61		$1,009.1472	$1,009.15	$1,009.15	$1,009.20