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	$132.98	6.850%	$142.0891	$142.09	$142.10	$142.10
Purchase #2	$175.67	7.854%	$189.4671	$189.47	$189.45	$189.50
Purchase #3	$139.55	9.564%	$152.8966	$152.90	$152.90	$152.90
Purchase #4	$151.67	7.230%	$162.6357	$162.64	$162.65	$162.60
Purchase #5	$145.90	11.259%	$162.3269	$162.33	$162.35	$162.30
Purchase #6	$28.86	4.529%	$30.1671	$30.17	$30.15	$30.20
Purchase #7	$55.55	10.247%	$61.2422	$61.24	$61.25	$61.20
7 purchase totals =	$830.18		$900.8247	$900.84	$900.85	$900.80