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	$50.84	13.106%	$57.5031	$57.50	$57.50	$57.50
Purchase #2	$98.46	10.621%	$108.9174	$108.92	$108.90	$108.90
Purchase #3	$173.32	10.801%	$192.0403	$192.04	$192.05	$192.00
Purchase #4	$237.80	11.191%	$264.4122	$264.41	$264.40	$264.40
Purchase #5	$50.34	4.228%	$52.4684	$52.47	$52.45	$52.50
Purchase #6	$17.31	9.379%	$18.9335	$18.93	$18.95	$18.90
Purchase #7	$110.32	12.378%	$123.9754	$123.98	$124.00	$124.00
7 purchase totals =	$738.39		$818.2503	$818.25	$818.25	$818.20