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	$40.42	6.283%	$42.9596	$42.96	$42.95	$43.00
Purchase #2	$80.67	8.546%	$87.5641	$87.56	$87.55	$87.60
Purchase #3	$30.59	10.532%	$33.8117	$33.81	$33.80	$33.80
Purchase #4	$100.68	4.300%	$105.0092	$105.01	$105.00	$105.00
Purchase #5	$79.73	4.688%	$83.4677	$83.47	$83.45	$83.50
Purchase #6	$57.97	5.631%	$61.2343	$61.23	$61.25	$61.20
Purchase #7	$116.57	8.326%	$126.2756	$126.28	$126.30	$126.30
7 purchase totals =	$506.63		$540.3222	$540.32	$540.30	$540.40