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	$136.69	11.382%	$152.2481	$152.25	$152.25	$152.20
Purchase #2	$217.96	9.233%	$238.0842	$238.08	$238.10	$238.10
Purchase #3	$211.26	10.335%	$233.0937	$233.09	$233.10	$233.10
Purchase #4	$35.75	10.773%	$39.6013	$39.60	$39.60	$39.60
Purchase #5	$164.49	12.568%	$185.1631	$185.16	$185.15	$185.20
Purchase #6	$180.56	12.679%	$203.4532	$203.45	$203.45	$203.50
Purchase #7	$167.43	11.571%	$186.8033	$186.80	$186.80	$186.80
7 purchase totals =	$1,114.14		$1,238.4469	$1,238.43	$1,238.45	$1,238.50