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	$234.56	10.122%	$258.3022	$258.30	$258.30	$258.30
Purchase #2	$204.67	5.273%	$215.4622	$215.46	$215.45	$215.50
Purchase #3	$45.25	11.719%	$50.5528	$50.55	$50.55	$50.60
Purchase #4	$55.25	13.182%	$62.5331	$62.53	$62.55	$62.50
Purchase #5	$154.32	10.421%	$170.4017	$170.40	$170.40	$170.40
Purchase #6	$235.59	3.611%	$244.0972	$244.10	$244.10	$244.10
Purchase #7	$6.56	3.339%	$6.779	$6.78	$6.80	$6.80
7 purchase totals =	$936.20		$1,008.1282	$1,008.12	$1,008.15	$1,008.20