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	$57.92	6.307%	$61.573	$61.57	$61.55	$61.60
Purchase #2	$202.44	3.187%	$208.8918	$208.89	$208.90	$208.90
Purchase #3	$41.71	5.103%	$43.8385	$43.84	$43.85	$43.80
Purchase #4	$141.94	6.117%	$150.6225	$150.62	$150.60	$150.60
Purchase #5	$85.61	5.217%	$90.0763	$90.08	$90.10	$90.10
Purchase #6	$121.42	5.569%	$128.1819	$128.18	$128.20	$128.20
Purchase #7	$62.36	3.752%	$64.6997	$64.70	$64.70	$64.70
7 purchase totals =	$713.40		$747.8837	$747.88	$747.90	$747.90