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	$224.34	6.320%	$238.5183	$238.52	$238.50	$238.50
Purchase #2	$201.38	7.622%	$216.7292	$216.73	$216.75	$216.70
Purchase #3	$84.64	7.478%	$90.9694	$90.97	$90.95	$91.00
Purchase #4	$66.70	5.494%	$70.3645	$70.36	$70.35	$70.40
Purchase #5	$123.60	3.183%	$127.5342	$127.53	$127.55	$127.50
Purchase #6	$144.46	13.834%	$164.4446	$164.44	$164.45	$164.40
Purchase #7	$205.50	9.274%	$224.5581	$224.56	$224.55	$224.60
7 purchase totals =	$1,050.62		$1,133.1183	$1,133.11	$1,133.10	$1,133.10