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	$39.57	5.782%	$41.8579	$41.86	$41.85	$41.90
Purchase #2	$236.98	7.238%	$254.1326	$254.13	$254.15	$254.10
Purchase #3	$96.50	7.225%	$103.4721	$103.47	$103.45	$103.50
Purchase #4	$183.88	6.627%	$196.0657	$196.07	$196.05	$196.10
Purchase #5	$204.64	7.296%	$219.5705	$219.57	$219.55	$219.60
Purchase #6	$83.68	11.798%	$93.5526	$93.55	$93.55	$93.60
Purchase #7	$85.29	7.116%	$91.3592	$91.36	$91.35	$91.40
7 purchase totals =	$930.54		$1,000.0106	$1,000.01	$999.95	$1,000.20