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	$73.76	13.364%	$83.6173	$83.62	$83.60	$83.60
Purchase #2	$142.81	6.678%	$152.3469	$152.35	$152.35	$152.30
Purchase #3	$57.31	9.369%	$62.6794	$62.68	$62.70	$62.70
Purchase #4	$53.84	3.281%	$55.6065	$55.61	$55.60	$55.60
Purchase #5	$102.86	11.635%	$114.8278	$114.83	$114.85	$114.80
Purchase #6	$39.76	7.810%	$42.8653	$42.87	$42.85	$42.90
Purchase #7	$75.82	6.733%	$80.925	$80.93	$80.95	$80.90
7 purchase totals =	$546.16		$592.8682	$592.89	$592.90	$592.80