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	$202.70	10.173%	$223.3207	$223.32	$223.30	$223.30
Purchase #2	$54.94	13.666%	$62.4481	$62.45	$62.45	$62.40
Purchase #3	$103.94	4.316%	$108.4261	$108.43	$108.45	$108.40
Purchase #4	$36.70	9.586%	$40.2181	$40.22	$40.20	$40.20
Purchase #5	$40.91	8.704%	$44.4708	$44.47	$44.45	$44.50
Purchase #6	$233.60	7.419%	$250.9308	$250.93	$250.95	$250.90
Purchase #7	$181.50	4.105%	$188.9506	$188.95	$188.95	$189.00
7 purchase totals =	$854.29		$918.7652	$918.77	$918.75	$918.70