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	$19.54	4.359%	$20.3917	$20.39	$20.40	$20.40
Purchase #2	$85.52	3.301%	$88.343	$88.34	$88.35	$88.30
Purchase #3	$95.77	4.693%	$100.2645	$100.26	$100.25	$100.30
Purchase #4	$236.45	12.306%	$265.5475	$265.55	$265.55	$265.50
Purchase #5	$137.32	10.873%	$152.2508	$152.25	$152.25	$152.30
Purchase #6	$162.29	4.755%	$170.0069	$170.01	$170.00	$170.00
Purchase #7	$10.67	13.210%	$12.0795	$12.08	$12.10	$12.10
7 purchase totals =	$747.56		$808.8839	$808.88	$808.90	$808.90