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	$60.50	9.672%	$66.3516	$66.35	$66.35	$66.40
Purchase #2	$223.79	9.470%	$244.9829	$244.98	$245.00	$245.00
Purchase #3	$184.37	3.804%	$191.3834	$191.38	$191.40	$191.40
Purchase #4	$177.82	10.359%	$196.2404	$196.24	$196.25	$196.20
Purchase #5	$187.70	5.555%	$198.1267	$198.13	$198.15	$198.10
Purchase #6	$147.37	8.111%	$159.3232	$159.32	$159.30	$159.30
Purchase #7	$229.27	13.766%	$260.8313	$260.83	$260.85	$260.80
7 purchase totals =	$1,210.82		$1,317.2395	$1,317.23	$1,317.30	$1,317.20