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	$115.46	11.642%	$128.9019	$128.90	$128.90	$128.90
Purchase #2	$189.49	7.151%	$203.0404	$203.04	$203.05	$203.00
Purchase #3	$152.37	13.821%	$173.4291	$173.43	$173.45	$173.40
Purchase #4	$23.30	3.320%	$24.0736	$24.07	$24.05	$24.10
Purchase #5	$54.95	11.497%	$61.2676	$61.27	$61.25	$61.30
Purchase #6	$124.78	13.675%	$141.8437	$141.84	$141.85	$141.80
Purchase #7	$185.98	5.794%	$196.7557	$196.76	$196.75	$196.80
7 purchase totals =	$846.33		$929.3120	$929.31	$929.30	$929.30