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	$242.85	6.598%	$258.8732	$258.87	$258.85	$258.90
Purchase #2	$138.33	13.108%	$156.4623	$156.46	$156.45	$156.50
Purchase #3	$213.59	13.690%	$242.8305	$242.83	$242.85	$242.80
Purchase #4	$96.87	5.693%	$102.3848	$102.38	$102.40	$102.40
Purchase #5	$91.90	13.840%	$104.619	$104.62	$104.60	$104.60
Purchase #6	$134.47	3.666%	$139.3997	$139.40	$139.40	$139.40
Purchase #7	$223.73	9.286%	$244.5056	$244.51	$244.50	$244.50
7 purchase totals =	$1,141.74		$1,249.0751	$1,249.07	$1,249.05	$1,249.10