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	$35.59	13.668%	$40.4544	$40.45	$40.45	$40.50
Purchase #2	$197.75	11.707%	$220.9006	$220.90	$220.90	$220.90
Purchase #3	$124.78	6.808%	$133.275	$133.28	$133.30	$133.30
Purchase #4	$115.49	8.810%	$125.6647	$125.66	$125.65	$125.70
Purchase #5	$198.50	10.698%	$219.7355	$219.74	$219.75	$219.70
Purchase #6	$156.60	9.556%	$171.5647	$171.56	$171.55	$171.60
Purchase #7	$176.72	13.689%	$200.9112	$200.91	$200.90	$200.90
7 purchase totals =	$1,005.43		$1,112.5061	$1,112.50	$1,112.50	$1,112.60