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	$82.51	8.757%	$89.7354	$89.74	$89.75	$89.70
Purchase #2	$148.87	10.838%	$165.0045	$165.00	$165.00	$165.00
Purchase #3	$99.90	3.628%	$103.5244	$103.52	$103.50	$103.50
Purchase #4	$199.69	4.784%	$209.2432	$209.24	$209.25	$209.20
Purchase #5	$125.65	7.834%	$135.4934	$135.49	$135.50	$135.50
Purchase #6	$189.33	13.863%	$215.5768	$215.58	$215.60	$215.60
Purchase #7	$93.50	8.841%	$101.7663	$101.77	$101.75	$101.80
7 purchase totals =	$939.45		$1,020.3440	$1,020.34	$1,020.35	$1,020.30