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	$147.90	12.493%	$166.3771	$166.38	$166.40	$166.40
Purchase #2	$145.80	8.811%	$158.6464	$158.65	$158.65	$158.60
Purchase #3	$42.56	6.314%	$45.2472	$45.25	$45.25	$45.20
Purchase #4	$69.31	11.270%	$77.1212	$77.12	$77.10	$77.10
Purchase #5	$86.92	13.426%	$98.5899	$98.59	$98.60	$98.60
Purchase #6	$84.34	8.713%	$91.6885	$91.69	$91.70	$91.70
Purchase #7	$187.31	11.117%	$208.1333	$208.13	$208.15	$208.10
7 purchase totals =	$764.14		$845.8036	$845.81	$845.85	$845.70