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	$95.88	12.405%	$107.7739	$107.77	$107.75	$107.80
Purchase #2	$59.59	12.364%	$66.9577	$66.96	$66.95	$67.00
Purchase #3	$176.64	5.259%	$185.9295	$185.93	$185.95	$185.90
Purchase #4	$61.89	7.290%	$66.4018	$66.40	$66.40	$66.40
Purchase #5	$184.28	5.295%	$194.0376	$194.04	$194.05	$194.00
Purchase #6	$212.29	13.207%	$240.3271	$240.33	$240.35	$240.30
Purchase #7	$127.35	11.103%	$141.4897	$141.49	$141.50	$141.50
7 purchase totals =	$917.92		$1,002.9173	$1,002.92	$1,002.95	$1,002.90