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	$102.36	6.757%	$109.2765	$109.28	$109.30	$109.30
Purchase #2	$17.73	8.832%	$19.2959	$19.30	$19.30	$19.30
Purchase #3	$156.70	3.182%	$161.6862	$161.69	$161.70	$161.70
Purchase #4	$249.60	12.243%	$280.1585	$280.16	$280.15	$280.20
Purchase #5	$183.96	11.705%	$205.4925	$205.49	$205.50	$205.50
Purchase #6	$204.53	11.428%	$227.9037	$227.90	$227.90	$227.90
Purchase #7	$196.61	13.661%	$223.4689	$223.47	$223.45	$223.50
7 purchase totals =	$1,111.49		$1,227.2822	$1,227.29	$1,227.30	$1,227.40