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	$80.32	10.541%	$88.7865	$88.79	$88.80	$88.80
Purchase #2	$206.98	13.489%	$234.8995	$234.90	$234.90	$234.90
Purchase #3	$118.48	9.795%	$130.0851	$130.09	$130.10	$130.10
Purchase #4	$74.52	5.413%	$78.5538	$78.55	$78.55	$78.60
Purchase #5	$142.92	11.604%	$159.5044	$159.50	$159.50	$159.50
Purchase #6	$165.83	11.317%	$184.597	$184.60	$184.60	$184.60
Purchase #7	$62.61	5.537%	$66.0767	$66.08	$66.10	$66.10
7 purchase totals =	$851.66		$942.5030	$942.51	$942.55	$942.60