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	$81.93	10.433%	$90.4778	$90.48	$90.50	$90.50
Purchase #2	$203.42	10.660%	$225.1046	$225.10	$225.10	$225.10
Purchase #3	$185.83	11.106%	$206.4683	$206.47	$206.45	$206.50
Purchase #4	$44.70	11.183%	$49.6988	$49.70	$49.70	$49.70
Purchase #5	$112.81	13.257%	$127.7652	$127.77	$127.75	$127.80
Purchase #6	$69.75	3.735%	$72.3552	$72.36	$72.35	$72.40
Purchase #7	$190.46	3.300%	$196.7452	$196.75	$196.75	$196.70
7 purchase totals =	$888.90		$968.6151	$968.63	$968.60	$968.70