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	$100.42	4.331%	$104.7692	$104.77	$104.75	$104.80
Purchase #2	$118.77	10.146%	$130.8204	$130.82	$130.80	$130.80
Purchase #3	$58.76	11.261%	$65.377	$65.38	$65.40	$65.40
Purchase #4	$141.51	12.704%	$159.4874	$159.49	$159.50	$159.50
Purchase #5	$163.54	4.860%	$171.488	$171.49	$171.50	$171.50
Purchase #6	$170.76	5.388%	$179.9605	$179.96	$179.95	$180.00
Purchase #7	$89.80	12.240%	$100.7915	$100.79	$100.80	$100.80
7 purchase totals =	$843.56		$912.6940	$912.70	$912.70	$912.80