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	$28.81	6.279%	$30.619	$30.62	$30.60	$30.60
Purchase #2	$196.89	13.152%	$222.785	$222.79	$222.80	$222.80
Purchase #3	$127.31	11.718%	$142.2282	$142.23	$142.25	$142.20
Purchase #4	$134.75	5.558%	$142.2394	$142.24	$142.25	$142.20
Purchase #5	$200.74	11.537%	$223.8994	$223.90	$223.90	$223.90
Purchase #6	$176.29	3.390%	$182.2662	$182.27	$182.25	$182.30
Purchase #7	$239.84	4.664%	$251.0261	$251.03	$251.05	$251.00
7 purchase totals =	$1,104.63		$1,195.0633	$1,195.08	$1,195.10	$1,195.00