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	$237.91	4.356%	$248.2734	$248.27	$248.25	$248.30
Purchase #2	$25.56	10.443%	$28.2292	$28.23	$28.25	$28.20
Purchase #3	$150.83	11.200%	$167.723	$167.72	$167.70	$167.70
Purchase #4	$234.31	5.851%	$248.0195	$248.02	$248.00	$248.00
Purchase #5	$68.28	4.695%	$71.4857	$71.49	$71.50	$71.50
Purchase #6	$66.61	8.869%	$72.5176	$72.52	$72.50	$72.50
Purchase #7	$114.96	11.694%	$128.4034	$128.40	$128.40	$128.40
7 purchase totals =	$898.46		$964.6518	$964.65	$964.60	$964.60