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	$49.67	13.582%	$56.4162	$56.42	$56.40	$56.40
Purchase #2	$146.43	10.825%	$162.281	$162.28	$162.30	$162.30
Purchase #3	$247.44	12.575%	$278.5556	$278.56	$278.55	$278.60
Purchase #4	$220.41	9.523%	$241.3996	$241.40	$241.40	$241.40
Purchase #5	$174.82	8.531%	$189.7339	$189.73	$189.75	$189.70
Purchase #6	$54.33	5.142%	$57.1236	$57.12	$57.10	$57.10
Purchase #7	$80.43	12.602%	$90.5658	$90.57	$90.55	$90.60
7 purchase totals =	$973.53		$1,076.0757	$1,076.08	$1,076.05	$1,076.10