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	$53.81	4.872%	$56.4316	$56.43	$56.45	$56.40
Purchase #2	$194.75	4.181%	$202.8925	$202.89	$202.90	$202.90
Purchase #3	$163.50	5.332%	$172.2178	$172.22	$172.20	$172.20
Purchase #4	$144.73	11.343%	$161.1467	$161.15	$161.15	$161.10
Purchase #5	$117.35	5.219%	$123.4745	$123.47	$123.45	$123.50
Purchase #6	$88.48	12.645%	$99.6683	$99.67	$99.65	$99.70
Purchase #7	$148.31	13.772%	$168.7353	$168.74	$168.75	$168.70
7 purchase totals =	$910.93		$984.5667	$984.57	$984.55	$984.50