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	$205.75	3.161%	$212.2538	$212.25	$212.25	$212.30
Purchase #2	$99.80	4.665%	$104.4557	$104.46	$104.45	$104.50
Purchase #3	$125.92	10.715%	$139.4123	$139.41	$139.40	$139.40
Purchase #4	$116.43	6.387%	$123.8664	$123.87	$123.85	$123.90
Purchase #5	$198.45	12.608%	$223.4706	$223.47	$223.45	$223.50
Purchase #6	$61.84	8.804%	$67.2844	$67.28	$67.30	$67.30
Purchase #7	$83.59	10.556%	$92.4138	$92.41	$92.40	$92.40
7 purchase totals =	$891.78		$963.1570	$963.15	$963.10	$963.30