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	$91.47	3.755%	$94.9047	$94.90	$94.90	$94.90
Purchase #2	$244.71	11.375%	$272.5458	$272.55	$272.55	$272.50
Purchase #3	$79.42	11.330%	$88.4183	$88.42	$88.40	$88.40
Purchase #4	$140.50	10.162%	$154.7776	$154.78	$154.80	$154.80
Purchase #5	$46.67	7.719%	$50.2725	$50.27	$50.25	$50.30
Purchase #6	$233.80	7.143%	$250.5003	$250.50	$250.50	$250.50
Purchase #7	$104.27	6.847%	$111.4094	$111.41	$111.40	$111.40
7 purchase totals =	$940.84		$1,022.8286	$1,022.83	$1,022.80	$1,022.80