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	$41.54	5.740%	$43.9244	$43.92	$43.90	$43.90
Purchase #2	$58.90	5.556%	$62.1725	$62.17	$62.15	$62.20
Purchase #3	$48.57	4.482%	$50.7469	$50.75	$50.75	$50.70
Purchase #4	$33.60	11.392%	$37.4277	$37.43	$37.45	$37.40
Purchase #5	$131.47	6.498%	$140.0129	$140.01	$140.00	$140.00
Purchase #6	$43.98	9.379%	$48.1049	$48.10	$48.10	$48.10
Purchase #7	$126.89	6.852%	$135.5845	$135.58	$135.60	$135.60
7 purchase totals =	$484.95		$517.9738	$517.96	$517.95	$517.90