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	$170.76	5.697%	$180.4882	$180.49	$180.50	$180.50
Purchase #2	$212.33	10.263%	$234.1214	$234.12	$234.10	$234.10
Purchase #3	$45.69	6.720%	$48.7604	$48.76	$48.75	$48.80
Purchase #4	$100.81	10.636%	$111.5322	$111.53	$111.55	$111.50
Purchase #5	$180.65	6.576%	$192.5295	$192.53	$192.55	$192.50
Purchase #6	$198.86	10.256%	$219.2551	$219.26	$219.25	$219.30
Purchase #7	$23.61	7.603%	$25.4051	$25.41	$25.40	$25.40
7 purchase totals =	$932.71		$1,012.0919	$1,012.10	$1,012.10	$1,012.10