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	$19.41	3.335%	$20.0573	$20.06	$20.05	$20.10
Purchase #2	$31.63	6.381%	$33.6483	$33.65	$33.65	$33.60
Purchase #3	$118.92	12.605%	$133.9099	$133.91	$133.90	$133.90
Purchase #4	$168.53	13.124%	$190.6479	$190.65	$190.65	$190.60
Purchase #5	$90.46	5.675%	$95.5936	$95.59	$95.60	$95.60
Purchase #6	$43.91	5.164%	$46.1775	$46.18	$46.20	$46.20
Purchase #7	$241.45	13.384%	$273.7657	$273.77	$273.75	$273.80
7 purchase totals =	$714.31		$793.8002	$793.81	$793.80	$793.80