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	$6.59	10.422%	$7.2768	$7.28	$7.30	$7.30
Purchase #2	$145.33	9.829%	$159.6145	$159.61	$159.60	$159.60
Purchase #3	$52.91	4.526%	$55.3047	$55.30	$55.30	$55.30
Purchase #4	$238.66	7.351%	$256.2039	$256.20	$256.20	$256.20
Purchase #5	$235.61	10.218%	$259.6846	$259.68	$259.70	$259.70
Purchase #6	$86.77	12.778%	$97.8575	$97.86	$97.85	$97.90
Purchase #7	$165.64	9.826%	$181.9158	$181.92	$181.90	$181.90
7 purchase totals =	$931.51		$1,017.8578	$1,017.85	$1,017.85	$1,017.90