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	$170.56	7.315%	$183.0365	$183.04	$183.05	$183.00
Purchase #2	$56.92	4.762%	$59.6305	$59.63	$59.65	$59.60
Purchase #3	$44.58	8.285%	$48.2735	$48.27	$48.25	$48.30
Purchase #4	$62.86	4.349%	$65.5938	$65.59	$65.60	$65.60
Purchase #5	$128.30	7.440%	$137.8455	$137.85	$137.85	$137.80
Purchase #6	$64.51	5.250%	$67.8968	$67.90	$67.90	$67.90
Purchase #7	$81.88	10.415%	$90.4078	$90.41	$90.40	$90.40
7 purchase totals =	$609.61		$652.6844	$652.69	$652.70	$652.60