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	$23.82	9.703%	$26.1313	$26.13	$26.15	$26.10
Purchase #2	$116.95	5.688%	$123.6021	$123.60	$123.60	$123.60
Purchase #3	$238.73	12.291%	$268.0723	$268.07	$268.05	$268.10
Purchase #4	$85.69	4.570%	$89.606	$89.61	$89.60	$89.60
Purchase #5	$72.71	9.773%	$79.8159	$79.82	$79.80	$79.80
Purchase #6	$92.31	7.858%	$99.5637	$99.56	$99.55	$99.60
Purchase #7	$205.41	11.369%	$228.7631	$228.76	$228.75	$228.80
7 purchase totals =	$835.62		$915.5544	$915.55	$915.50	$915.60