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	$89.98	10.683%	$99.5926	$99.59	$99.60	$99.60
Purchase #2	$59.31	9.312%	$64.8329	$64.83	$64.85	$64.80
Purchase #3	$13.46	7.556%	$14.477	$14.48	$14.50	$14.50
Purchase #4	$185.30	13.738%	$210.7565	$210.76	$210.75	$210.80
Purchase #5	$222.54	3.585%	$230.5181	$230.52	$230.50	$230.50
Purchase #6	$83.62	3.805%	$86.8017	$86.80	$86.80	$86.80
Purchase #7	$135.50	12.782%	$152.8196	$152.82	$152.80	$152.80
7 purchase totals =	$789.71		$859.7984	$859.80	$859.80	$859.80