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	$109.96	12.177%	$123.3498	$123.35	$123.35	$123.30
Purchase #2	$231.42	9.555%	$253.5322	$253.53	$253.55	$253.50
Purchase #3	$230.62	11.407%	$256.9268	$256.93	$256.95	$256.90
Purchase #4	$125.77	8.389%	$136.3208	$136.32	$136.30	$136.30
Purchase #5	$50.27	10.618%	$55.6077	$55.61	$55.60	$55.60
Purchase #6	$145.46	4.806%	$152.4508	$152.45	$152.45	$152.50
Purchase #7	$46.47	4.830%	$48.7145	$48.71	$48.70	$48.70
7 purchase totals =	$939.97		$1,026.9026	$1,026.90	$1,026.90	$1,026.80