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	$55.45	3.287%	$57.2726	$57.27	$57.25	$57.30
Purchase #2	$94.96	6.855%	$101.4695	$101.47	$101.45	$101.50
Purchase #3	$102.65	9.468%	$112.3689	$112.37	$112.35	$112.40
Purchase #4	$95.34	11.352%	$106.163	$106.16	$106.15	$106.20
Purchase #5	$159.37	5.575%	$168.2549	$168.25	$168.25	$168.30
Purchase #6	$168.77	4.338%	$176.0912	$176.09	$176.10	$176.10
Purchase #7	$98.94	13.748%	$112.5423	$112.54	$112.55	$112.50
7 purchase totals =	$775.48		$834.1624	$834.15	$834.10	$834.30