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	$39.81	6.702%	$42.4781	$42.48	$42.50	$42.50
Purchase #2	$233.98	13.398%	$265.3286	$265.33	$265.35	$265.30
Purchase #3	$62.89	13.531%	$71.3996	$71.40	$71.40	$71.40
Purchase #4	$213.41	7.806%	$230.0688	$230.07	$230.05	$230.10
Purchase #5	$87.35	8.730%	$94.9757	$94.98	$95.00	$95.00
Purchase #6	$159.34	13.547%	$180.9258	$180.93	$180.95	$180.90
Purchase #7	$81.42	11.318%	$90.6351	$90.64	$90.65	$90.60
7 purchase totals =	$878.20		$975.8117	$975.83	$975.90	$975.80