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	$72.43	10.125%	$79.7635	$79.76	$79.75	$79.80
Purchase #2	$211.73	10.248%	$233.4281	$233.43	$233.45	$233.40
Purchase #3	$250.28	3.284%	$258.4992	$258.50	$258.50	$258.50
Purchase #4	$64.45	13.144%	$72.9213	$72.92	$72.90	$72.90
Purchase #5	$81.45	5.486%	$85.9183	$85.92	$85.90	$85.90
Purchase #6	$242.25	8.408%	$262.6184	$262.62	$262.60	$262.60
Purchase #7	$125.72	3.786%	$130.4798	$130.48	$130.50	$130.50
7 purchase totals =	$1,048.31		$1,123.6286	$1,123.63	$1,123.60	$1,123.60