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	$236.32	12.824%	$266.6257	$266.63	$266.65	$266.60
Purchase #2	$151.40	3.376%	$156.5113	$156.51	$156.50	$156.50
Purchase #3	$236.65	3.327%	$244.5233	$244.52	$244.50	$244.50
Purchase #4	$152.86	12.801%	$172.4276	$172.43	$172.45	$172.40
Purchase #5	$55.89	3.529%	$57.8624	$57.86	$57.85	$57.90
Purchase #6	$188.42	9.626%	$206.5573	$206.56	$206.55	$206.60
Purchase #7	$222.42	9.286%	$243.0739	$243.07	$243.05	$243.10
7 purchase totals =	$1,243.96		$1,347.5815	$1,347.58	$1,347.55	$1,347.60