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	$199.46	13.223%	$225.8346	$225.83	$225.85	$225.80
Purchase #2	$111.77	8.483%	$121.2514	$121.25	$121.25	$121.30
Purchase #3	$236.50	7.419%	$254.0459	$254.05	$254.05	$254.00
Purchase #4	$42.32	7.528%	$45.5058	$45.51	$45.50	$45.50
Purchase #5	$123.89	6.361%	$131.7706	$131.77	$131.75	$131.80
Purchase #6	$123.25	5.404%	$129.9104	$129.91	$129.90	$129.90
Purchase #7	$146.50	7.590%	$157.6194	$157.62	$157.60	$157.60
7 purchase totals =	$983.69		$1,065.9381	$1,065.94	$1,065.90	$1,065.90