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	$13.89	13.822%	$15.8099	$15.81	$15.80	$15.80
Purchase #2	$27.89	10.871%	$30.9219	$30.92	$30.90	$30.90
Purchase #3	$78.35	13.872%	$89.2187	$89.22	$89.20	$89.20
Purchase #4	$192.63	13.850%	$219.3093	$219.31	$219.30	$219.30
Purchase #5	$195.36	6.536%	$208.1287	$208.13	$208.15	$208.10
Purchase #6	$206.62	5.631%	$218.2548	$218.25	$218.25	$218.30
Purchase #7	$19.97	3.326%	$20.6342	$20.63	$20.65	$20.60
7 purchase totals =	$734.71		$802.2775	$802.27	$802.25	$802.20