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	$42.99	8.230%	$46.5281	$46.53	$46.55	$46.50
Purchase #2	$12.98	8.149%	$14.0377	$14.04	$14.05	$14.00
Purchase #3	$113.77	8.493%	$123.4325	$123.43	$123.45	$123.40
Purchase #4	$70.31	13.159%	$79.5621	$79.56	$79.55	$79.60
Purchase #5	$183.43	9.219%	$200.3404	$200.34	$200.35	$200.30
Purchase #6	$16.55	10.459%	$18.281	$18.28	$18.30	$18.30
Purchase #7	$49.72	12.348%	$55.8594	$55.86	$55.85	$55.90
7 purchase totals =	$489.75		$538.0412	$538.04	$538.10	$538.00