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	$55.78	6.490%	$59.4001	$59.40	$59.40	$59.40
Purchase #2	$250.94	3.633%	$260.0567	$260.06	$260.05	$260.10
Purchase #3	$209.92	13.631%	$238.5342	$238.53	$238.55	$238.50
Purchase #4	$153.47	11.551%	$171.1973	$171.20	$171.20	$171.20
Purchase #5	$192.42	6.547%	$205.0177	$205.02	$205.00	$205.00
Purchase #6	$101.64	12.466%	$114.3104	$114.31	$114.30	$114.30
Purchase #7	$128.49	6.834%	$137.271	$137.27	$137.25	$137.30
7 purchase totals =	$1,092.66		$1,185.7874	$1,185.79	$1,185.75	$1,185.80