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	$33.73	11.807%	$37.7125	$37.71	$37.70	$37.70
Purchase #2	$103.87	7.106%	$111.251	$111.25	$111.25	$111.30
Purchase #3	$69.75	6.814%	$74.5028	$74.50	$74.50	$74.50
Purchase #4	$132.88	13.243%	$150.4773	$150.48	$150.50	$150.50
Purchase #5	$87.53	9.272%	$95.6458	$95.65	$95.65	$95.60
Purchase #6	$52.48	7.108%	$56.2103	$56.21	$56.20	$56.20
Purchase #7	$85.87	12.467%	$96.5754	$96.58	$96.60	$96.60
7 purchase totals =	$566.11		$622.3751	$622.38	$622.40	$622.40