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	$126.83	13.761%	$144.2831	$144.28	$144.30	$144.30
Purchase #2	$32.70	6.738%	$34.9033	$34.90	$34.90	$34.90
Purchase #3	$99.83	9.519%	$109.3328	$109.33	$109.35	$109.30
Purchase #4	$182.28	6.606%	$194.3214	$194.32	$194.30	$194.30
Purchase #5	$169.99	9.350%	$185.8841	$185.88	$185.90	$185.90
Purchase #6	$135.28	4.761%	$141.7207	$141.72	$141.70	$141.70
Purchase #7	$152.28	4.421%	$159.0123	$159.01	$159.00	$159.00
7 purchase totals =	$899.19		$969.4577	$969.44	$969.45	$969.40