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	$7.30	10.104%	$8.0376	$8.04	$8.05	$8.00
Purchase #2	$130.68	13.302%	$148.0631	$148.06	$148.05	$148.10
Purchase #3	$79.85	13.783%	$90.8557	$90.86	$90.85	$90.90
Purchase #4	$37.62	12.419%	$42.292	$42.29	$42.30	$42.30
Purchase #5	$56.55	10.827%	$62.6727	$62.67	$62.65	$62.70
Purchase #6	$137.99	3.591%	$142.9452	$142.95	$142.95	$142.90
Purchase #7	$58.44	7.648%	$62.9095	$62.91	$62.90	$62.90
7 purchase totals =	$508.43		$557.7758	$557.78	$557.75	$557.80