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	$11.56	7.266%	$12.3999	$12.40	$12.40	$12.40
Purchase #2	$83.27	10.313%	$91.8576	$91.86	$91.85	$91.90
Purchase #3	$182.50	7.720%	$196.589	$196.59	$196.60	$196.60
Purchase #4	$116.50	3.518%	$120.5985	$120.60	$120.60	$120.60
Purchase #5	$141.63	8.254%	$153.3201	$153.32	$153.30	$153.30
Purchase #6	$82.51	13.362%	$93.535	$93.54	$93.55	$93.50
Purchase #7	$16.50	5.640%	$17.4306	$17.43	$17.45	$17.40
7 purchase totals =	$634.47		$685.7307	$685.74	$685.75	$685.70