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	$7.86	13.387%	$8.9122	$8.91	$8.90	$8.90
Purchase #2	$108.70	7.281%	$116.6144	$116.61	$116.60	$116.60
Purchase #3	$137.45	12.272%	$154.3179	$154.32	$154.30	$154.30
Purchase #4	$78.83	10.229%	$86.8935	$86.89	$86.90	$86.90
Purchase #5	$135.32	6.663%	$144.3364	$144.34	$144.35	$144.30
Purchase #6	$170.96	13.555%	$194.1336	$194.13	$194.15	$194.10
Purchase #7	$225.32	13.447%	$255.6188	$255.62	$255.60	$255.60
7 purchase totals =	$864.44		$960.8268	$960.82	$960.80	$960.70