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	$19.66	6.261%	$20.8909	$20.89	$20.90	$20.90
Purchase #2	$191.29	13.859%	$217.8009	$217.80	$217.80	$217.80
Purchase #3	$27.38	13.137%	$30.9769	$30.98	$31.00	$31.00
Purchase #4	$247.69	3.281%	$255.8167	$255.82	$255.80	$255.80
Purchase #5	$112.99	3.339%	$116.7627	$116.76	$116.75	$116.80
Purchase #6	$38.50	9.457%	$42.1409	$42.14	$42.15	$42.10
Purchase #7	$19.30	10.542%	$21.3346	$21.33	$21.35	$21.30
7 purchase totals =	$656.81		$705.7236	$705.72	$705.75	$705.70