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	$225.52	10.598%	$249.4206	$249.42	$249.40	$249.40
Purchase #2	$35.40	12.743%	$39.911	$39.91	$39.90	$39.90
Purchase #3	$110.87	9.820%	$121.7574	$121.76	$121.75	$121.80
Purchase #4	$153.66	11.305%	$171.0313	$171.03	$171.05	$171.00
Purchase #5	$72.59	13.645%	$82.4949	$82.49	$82.50	$82.50
Purchase #6	$114.59	12.466%	$128.8748	$128.87	$128.85	$128.90
Purchase #7	$120.93	13.744%	$137.5506	$137.55	$137.55	$137.60
7 purchase totals =	$833.56		$931.0406	$931.03	$931.00	$931.10