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	$205.51	5.421%	$216.6507	$216.65	$216.65	$216.70
Purchase #2	$178.94	3.731%	$185.6163	$185.62	$185.60	$185.60
Purchase #3	$107.82	6.551%	$114.8833	$114.88	$114.90	$114.90
Purchase #4	$81.59	10.468%	$90.1308	$90.13	$90.15	$90.10
Purchase #5	$136.60	10.393%	$150.7968	$150.80	$150.80	$150.80
Purchase #6	$26.37	11.645%	$29.4408	$29.44	$29.45	$29.40
Purchase #7	$53.78	12.590%	$60.5509	$60.55	$60.55	$60.60
7 purchase totals =	$790.61		$848.0696	$848.07	$848.10	$848.10