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	$57.77	11.617%	$64.4811	$64.48	$64.50	$64.50
Purchase #2	$131.56	11.608%	$146.8315	$146.83	$146.85	$146.80
Purchase #3	$77.75	5.487%	$82.0161	$82.02	$82.00	$82.00
Purchase #4	$54.86	4.377%	$57.2612	$57.26	$57.25	$57.30
Purchase #5	$173.67	11.836%	$194.2256	$194.23	$194.25	$194.20
Purchase #6	$40.34	7.373%	$43.3143	$43.31	$43.30	$43.30
Purchase #7	$60.29	4.414%	$62.9512	$62.95	$62.95	$63.00
7 purchase totals =	$596.24		$651.0810	$651.08	$651.10	$651.10