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	$29.96	4.423%	$31.2851	$31.29	$31.30	$31.30
Purchase #2	$45.99	13.818%	$52.3449	$52.34	$52.35	$52.30
Purchase #3	$160.80	6.176%	$170.731	$170.73	$170.75	$170.70
Purchase #4	$71.43	9.167%	$77.978	$77.98	$78.00	$78.00
Purchase #5	$14.42	4.497%	$15.0685	$15.07	$15.05	$15.10
Purchase #6	$137.37	10.863%	$152.2925	$152.29	$152.30	$152.30
Purchase #7	$116.36	9.588%	$127.5166	$127.52	$127.50	$127.50
7 purchase totals =	$576.33		$627.2166	$627.22	$627.25	$627.20