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	$162.99	10.547%	$180.1806	$180.18	$180.20	$180.20
Purchase #2	$205.34	7.200%	$220.1245	$220.12	$220.10	$220.10
Purchase #3	$72.66	13.402%	$82.3979	$82.40	$82.40	$82.40
Purchase #4	$78.98	13.514%	$89.6534	$89.65	$89.65	$89.70
Purchase #5	$177.27	7.188%	$190.0122	$190.01	$190.00	$190.00
Purchase #6	$32.40	13.173%	$36.6681	$36.67	$36.65	$36.70
Purchase #7	$201.34	4.227%	$209.8506	$209.85	$209.85	$209.90
7 purchase totals =	$930.98		$1,008.8873	$1,008.88	$1,008.85	$1,009.00