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	$54.83	3.123%	$56.5423	$56.54	$56.55	$56.50
Purchase #2	$137.47	9.161%	$150.0636	$150.06	$150.05	$150.10
Purchase #3	$193.86	10.407%	$214.035	$214.04	$214.05	$214.00
Purchase #4	$155.98	11.213%	$173.47	$173.47	$173.45	$173.50
Purchase #5	$6.93	7.498%	$7.4496	$7.45	$7.45	$7.40
Purchase #6	$141.39	6.333%	$150.3442	$150.34	$150.35	$150.30
Purchase #7	$100.33	11.282%	$111.6492	$111.65	$111.65	$111.60
7 purchase totals =	$790.79		$863.5539	$863.55	$863.55	$863.40