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	$38.43	11.573%	$42.8775	$42.88	$42.90	$42.90
Purchase #2	$28.27	3.725%	$29.3231	$29.32	$29.30	$29.30
Purchase #3	$147.70	8.109%	$159.677	$159.68	$159.70	$159.70
Purchase #4	$180.59	13.719%	$205.3651	$205.37	$205.35	$205.40
Purchase #5	$39.99	7.262%	$42.8941	$42.89	$42.90	$42.90
Purchase #6	$152.29	5.317%	$160.3873	$160.39	$160.40	$160.40
Purchase #7	$149.60	6.177%	$158.8408	$158.84	$158.85	$158.80
7 purchase totals =	$736.87		$799.3649	$799.37	$799.40	$799.40