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	$29.27	11.276%	$32.5705	$32.57	$32.55	$32.60
Purchase #2	$193.85	7.689%	$208.7551	$208.76	$208.75	$208.80
Purchase #3	$76.69	11.809%	$85.7463	$85.75	$85.75	$85.70
Purchase #4	$213.75	10.476%	$236.1425	$236.14	$236.15	$236.10
Purchase #5	$74.72	7.773%	$80.528	$80.53	$80.55	$80.50
Purchase #6	$65.61	8.784%	$71.3732	$71.37	$71.35	$71.40
Purchase #7	$137.80	4.574%	$144.103	$144.10	$144.10	$144.10
7 purchase totals =	$791.69		$859.2186	$859.22	$859.20	$859.20