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	$85.35	5.266%	$89.8445	$89.84	$89.85	$89.80
Purchase #2	$180.45	9.853%	$198.2297	$198.23	$198.25	$198.20
Purchase #3	$74.92	13.555%	$85.0754	$85.08	$85.10	$85.10
Purchase #4	$131.65	11.326%	$146.5607	$146.56	$146.55	$146.60
Purchase #5	$153.86	8.754%	$167.3289	$167.33	$167.35	$167.30
Purchase #6	$77.74	5.662%	$82.1416	$82.14	$82.15	$82.10
Purchase #7	$199.44	13.296%	$225.9575	$225.96	$225.95	$226.00
7 purchase totals =	$903.41		$995.1383	$995.14	$995.20	$995.10