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	$229.49	6.431%	$244.2485	$244.25	$244.25	$244.20
Purchase #2	$221.59	7.685%	$238.6192	$238.62	$238.60	$238.60
Purchase #3	$38.59	3.749%	$40.0367	$40.04	$40.05	$40.00
Purchase #4	$93.31	12.371%	$104.8534	$104.85	$104.85	$104.90
Purchase #5	$27.74	12.374%	$31.1725	$31.17	$31.15	$31.20
Purchase #6	$226.49	9.417%	$247.8186	$247.82	$247.80	$247.80
Purchase #7	$153.41	11.386%	$170.8773	$170.88	$170.90	$170.90
7 purchase totals =	$990.62		$1,077.6262	$1,077.63	$1,077.60	$1,077.60