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	$122.98	8.462%	$133.3866	$133.39	$133.40	$133.40
Purchase #2	$58.86	10.603%	$65.1009	$65.10	$65.10	$65.10
Purchase #3	$184.30	6.561%	$196.3919	$196.39	$196.40	$196.40
Purchase #4	$177.70	10.532%	$196.4154	$196.42	$196.40	$196.40
Purchase #5	$93.98	11.194%	$104.5001	$104.50	$104.50	$104.50
Purchase #6	$126.70	8.711%	$137.7368	$137.74	$137.75	$137.70
Purchase #7	$5.84	11.232%	$6.4959	$6.50	$6.50	$6.50
7 purchase totals =	$770.36		$840.0276	$840.04	$840.05	$840.00