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	$39.90	13.522%	$45.2953	$45.30	$45.30	$45.30
Purchase #2	$58.56	9.292%	$64.0014	$64.00	$64.00	$64.00
Purchase #3	$187.44	5.191%	$197.17	$197.17	$197.15	$197.20
Purchase #4	$99.96	12.374%	$112.3291	$112.33	$112.35	$112.30
Purchase #5	$235.80	13.766%	$268.2602	$268.26	$268.25	$268.30
Purchase #6	$80.40	12.343%	$90.3238	$90.32	$90.30	$90.30
Purchase #7	$39.39	4.251%	$41.0645	$41.06	$41.05	$41.10
7 purchase totals =	$741.45		$818.4443	$818.44	$818.40	$818.50