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	$55.31	5.562%	$58.3863	$58.39	$58.40	$58.40
Purchase #2	$100.27	5.170%	$105.454	$105.45	$105.45	$105.50
Purchase #3	$217.81	7.694%	$234.5683	$234.57	$234.55	$234.60
Purchase #4	$150.62	9.615%	$165.1021	$165.10	$165.10	$165.10
Purchase #5	$178.93	4.190%	$186.4272	$186.43	$186.45	$186.40
Purchase #6	$63.90	13.797%	$72.7163	$72.72	$72.70	$72.70
Purchase #7	$220.64	10.656%	$244.1514	$244.15	$244.15	$244.20
7 purchase totals =	$987.48		$1,066.8056	$1,066.81	$1,066.80	$1,066.90