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	$38.46	8.589%	$41.7633	$41.76	$41.75	$41.80
Purchase #2	$164.84	12.734%	$185.8307	$185.83	$185.85	$185.80
Purchase #3	$63.96	13.419%	$72.5428	$72.54	$72.55	$72.50
Purchase #4	$175.77	13.710%	$199.8681	$199.87	$199.85	$199.90
Purchase #5	$6.45	12.193%	$7.2364	$7.24	$7.25	$7.20
Purchase #6	$68.61	8.763%	$74.6223	$74.62	$74.60	$74.60
Purchase #7	$74.37	8.532%	$80.7152	$80.72	$80.70	$80.70
7 purchase totals =	$592.46		$662.5788	$662.58	$662.55	$662.50