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	$238.82	4.378%	$249.2755	$249.28	$249.30	$249.30
Purchase #2	$83.83	6.388%	$89.1851	$89.19	$89.20	$89.20
Purchase #3	$90.38	7.559%	$97.2118	$97.21	$97.20	$97.20
Purchase #4	$116.50	4.213%	$121.4081	$121.41	$121.40	$121.40
Purchase #5	$63.86	12.128%	$71.6049	$71.60	$71.60	$71.60
Purchase #6	$96.35	9.661%	$105.6584	$105.66	$105.65	$105.70
Purchase #7	$133.61	7.666%	$143.8525	$143.85	$143.85	$143.90
7 purchase totals =	$823.35		$878.1963	$878.20	$878.20	$878.30