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	$76.38	3.297%	$78.8982	$78.90	$78.90	$78.90
Purchase #2	$231.50	5.145%	$243.4107	$243.41	$243.40	$243.40
Purchase #3	$146.72	10.873%	$162.6729	$162.67	$162.65	$162.70
Purchase #4	$19.35	9.775%	$21.2415	$21.24	$21.25	$21.20
Purchase #5	$240.53	8.678%	$261.4032	$261.40	$261.40	$261.40
Purchase #6	$11.26	11.803%	$12.589	$12.59	$12.60	$12.60
Purchase #7	$183.42	9.203%	$200.3001	$200.30	$200.30	$200.30
7 purchase totals =	$909.16		$980.5156	$980.51	$980.50	$980.50