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	$242.49	6.497%	$258.2446	$258.24	$258.25	$258.20
Purchase #2	$115.98	9.784%	$127.3275	$127.33	$127.35	$127.30
Purchase #3	$152.39	8.431%	$165.238	$165.24	$165.25	$165.20
Purchase #4	$126.87	11.665%	$141.6694	$141.67	$141.65	$141.70
Purchase #5	$23.98	3.245%	$24.7582	$24.76	$24.75	$24.80
Purchase #6	$78.35	3.797%	$81.3249	$81.32	$81.30	$81.30
Purchase #7	$80.27	6.561%	$85.5365	$85.54	$85.55	$85.50
7 purchase totals =	$820.33		$884.0991	$884.10	$884.10	$884.00