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	$49.98	3.816%	$51.8872	$51.89	$51.90	$51.90
Purchase #2	$182.59	12.493%	$205.401	$205.40	$205.40	$205.40
Purchase #3	$84.57	7.243%	$90.6954	$90.70	$90.70	$90.70
Purchase #4	$145.67	6.727%	$155.4692	$155.47	$155.45	$155.50
Purchase #5	$65.52	12.415%	$73.6543	$73.65	$73.65	$73.70
Purchase #6	$37.39	13.123%	$42.2967	$42.30	$42.30	$42.30
Purchase #7	$155.90	11.293%	$173.5058	$173.51	$173.50	$173.50
7 purchase totals =	$721.62		$792.9096	$792.92	$792.90	$793.00