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	$102.59	12.844%	$115.7667	$115.77	$115.75	$115.80
Purchase #2	$61.77	9.399%	$67.5758	$67.58	$67.60	$67.60
Purchase #3	$217.27	7.483%	$233.5283	$233.53	$233.55	$233.50
Purchase #4	$189.78	3.632%	$196.6728	$196.67	$196.65	$196.70
Purchase #5	$114.35	8.345%	$123.8925	$123.89	$123.90	$123.90
Purchase #6	$43.76	8.463%	$47.4634	$47.46	$47.45	$47.50
Purchase #7	$74.68	11.840%	$83.5221	$83.52	$83.50	$83.50
7 purchase totals =	$804.20		$868.4216	$868.42	$868.40	$868.50