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	$9.59	11.489%	$10.6918	$10.69	$10.70	$10.70
Purchase #2	$194.79	7.381%	$209.1674	$209.17	$209.15	$209.20
Purchase #3	$206.65	8.832%	$224.9013	$224.90	$224.90	$224.90
Purchase #4	$196.42	10.213%	$216.4804	$216.48	$216.50	$216.50
Purchase #5	$165.28	12.208%	$185.4574	$185.46	$185.45	$185.50
Purchase #6	$247.58	13.289%	$280.4809	$280.48	$280.50	$280.50
Purchase #7	$32.30	8.509%	$35.0484	$35.05	$35.05	$35.00
7 purchase totals =	$1,052.61		$1,162.2276	$1,162.23	$1,162.25	$1,162.30