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	$149.59	11.805%	$167.2491	$167.25	$167.25	$167.20
Purchase #2	$47.45	8.695%	$51.5758	$51.58	$51.60	$51.60
Purchase #3	$96.90	6.722%	$103.4136	$103.41	$103.40	$103.40
Purchase #4	$98.31	3.621%	$101.8698	$101.87	$101.85	$101.90
Purchase #5	$43.78	3.364%	$45.2528	$45.25	$45.25	$45.30
Purchase #6	$96.37	8.467%	$104.5296	$104.53	$104.55	$104.50
Purchase #7	$247.45	3.106%	$255.1358	$255.14	$255.15	$255.10
7 purchase totals =	$779.85		$829.0265	$829.03	$829.05	$829.00