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	$244.83	11.331%	$272.5717	$272.57	$272.55	$272.60
Purchase #2	$28.78	10.422%	$31.7795	$31.78	$31.80	$31.80
Purchase #3	$66.31	7.135%	$71.0412	$71.04	$71.05	$71.00
Purchase #4	$51.82	5.263%	$54.5473	$54.55	$54.55	$54.50
Purchase #5	$228.79	13.197%	$258.9834	$258.98	$259.00	$259.00
Purchase #6	$164.77	11.161%	$183.16	$183.16	$183.15	$183.20
Purchase #7	$159.91	4.695%	$167.4178	$167.42	$167.40	$167.40
7 purchase totals =	$945.21		$1,039.5009	$1,039.50	$1,039.50	$1,039.50