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	$88.64	13.704%	$100.7872	$100.79	$100.80	$100.80
Purchase #2	$212.34	10.226%	$234.0539	$234.05	$234.05	$234.10
Purchase #3	$130.55	8.341%	$141.4392	$141.44	$141.45	$141.40
Purchase #4	$36.43	4.541%	$38.0843	$38.08	$38.10	$38.10
Purchase #5	$81.38	11.768%	$90.9568	$90.96	$90.95	$91.00
Purchase #6	$196.44	5.611%	$207.4622	$207.46	$207.45	$207.50
Purchase #7	$77.75	6.630%	$82.9048	$82.90	$82.90	$82.90
7 purchase totals =	$823.53		$895.6884	$895.68	$895.70	$895.80