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	$123.35	10.299%	$136.0538	$136.05	$136.05	$136.10
Purchase #2	$32.30	3.235%	$33.3449	$33.34	$33.35	$33.30
Purchase #3	$116.31	10.467%	$128.4842	$128.48	$128.50	$128.50
Purchase #4	$20.60	11.632%	$22.9962	$23.00	$23.00	$23.00
Purchase #5	$154.66	8.282%	$167.4689	$167.47	$167.45	$167.50
Purchase #6	$140.90	12.671%	$158.7534	$158.75	$158.75	$158.80
Purchase #7	$165.28	10.303%	$182.3088	$182.31	$182.30	$182.30
7 purchase totals =	$753.40		$829.4102	$829.40	$829.40	$829.50