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	$100.73	10.830%	$111.6391	$111.64	$111.65	$111.60
Purchase #2	$118.61	10.640%	$131.2301	$131.23	$131.25	$131.20
Purchase #3	$196.28	6.395%	$208.8321	$208.83	$208.85	$208.80
Purchase #4	$75.28	11.620%	$84.0275	$84.03	$84.05	$84.00
Purchase #5	$7.30	3.262%	$7.5381	$7.54	$7.55	$7.50
Purchase #6	$234.33	6.597%	$249.7888	$249.79	$249.80	$249.80
Purchase #7	$39.62	6.816%	$42.3205	$42.32	$42.30	$42.30
7 purchase totals =	$772.15		$835.3762	$835.38	$835.45	$835.20