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	$54.78	4.230%	$57.0972	$57.10	$57.10	$57.10
Purchase #2	$75.27	5.234%	$79.2096	$79.21	$79.20	$79.20
Purchase #3	$44.42	5.495%	$46.8609	$46.86	$46.85	$46.90
Purchase #4	$158.85	12.443%	$178.6157	$178.62	$178.60	$178.60
Purchase #5	$83.78	7.765%	$90.2855	$90.29	$90.30	$90.30
Purchase #6	$73.40	12.321%	$82.4436	$82.44	$82.45	$82.40
Purchase #7	$71.56	6.151%	$75.9617	$75.96	$75.95	$76.00
7 purchase totals =	$562.06		$610.4742	$610.48	$610.45	$610.50