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	$159.70	3.661%	$165.5466	$165.55	$165.55	$165.50
Purchase #2	$124.52	10.511%	$137.6083	$137.61	$137.60	$137.60
Purchase #3	$220.93	13.414%	$250.5656	$250.57	$250.55	$250.60
Purchase #4	$115.38	6.416%	$122.7828	$122.78	$122.80	$122.80
Purchase #5	$56.36	3.703%	$58.447	$58.45	$58.45	$58.40
Purchase #6	$82.77	3.240%	$85.4517	$85.45	$85.45	$85.50
Purchase #7	$233.56	10.698%	$258.5462	$258.55	$258.55	$258.50
7 purchase totals =	$993.22		$1,078.9482	$1,078.96	$1,078.95	$1,078.90