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	$100.92	6.405%	$107.3839	$107.38	$107.40	$107.40
Purchase #2	$73.94	10.140%	$81.4375	$81.44	$81.45	$81.40
Purchase #3	$238.95	11.251%	$265.8343	$265.83	$265.85	$265.80
Purchase #4	$147.73	11.306%	$164.4324	$164.43	$164.45	$164.40
Purchase #5	$72.29	8.760%	$78.6226	$78.62	$78.60	$78.60
Purchase #6	$59.84	7.849%	$64.5368	$64.54	$64.55	$64.50
Purchase #7	$51.73	8.489%	$56.1214	$56.12	$56.10	$56.10
7 purchase totals =	$745.40		$818.3689	$818.36	$818.40	$818.20