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	$190.80	12.835%	$215.2892	$215.29	$215.30	$215.30
Purchase #2	$117.79	11.259%	$131.052	$131.05	$131.05	$131.10
Purchase #3	$146.56	9.572%	$160.5887	$160.59	$160.60	$160.60
Purchase #4	$126.50	4.164%	$131.7675	$131.77	$131.75	$131.80
Purchase #5	$19.44	7.258%	$20.851	$20.85	$20.85	$20.90
Purchase #6	$165.88	9.862%	$182.2391	$182.24	$182.25	$182.20
Purchase #7	$106.91	10.346%	$117.9709	$117.97	$117.95	$118.00
7 purchase totals =	$873.88		$959.7584	$959.76	$959.75	$959.90