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	$125.36	4.410%	$130.8884	$130.89	$130.90	$130.90
Purchase #2	$51.72	5.256%	$54.4384	$54.44	$54.45	$54.40
Purchase #3	$40.64	5.122%	$42.7216	$42.72	$42.70	$42.70
Purchase #4	$191.27	13.699%	$217.4721	$217.47	$217.45	$217.50
Purchase #5	$52.62	3.403%	$54.4107	$54.41	$54.40	$54.40
Purchase #6	$94.69	13.277%	$107.262	$107.26	$107.25	$107.30
Purchase #7	$35.58	3.217%	$36.7246	$36.72	$36.70	$36.70
7 purchase totals =	$591.88		$643.9178	$643.91	$643.85	$643.90