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	$157.56	5.633%	$166.4354	$166.44	$166.45	$166.40
Purchase #2	$166.61	11.845%	$186.345	$186.35	$186.35	$186.30
Purchase #3	$190.83	4.837%	$200.0604	$200.06	$200.05	$200.10
Purchase #4	$126.61	8.678%	$137.5972	$137.60	$137.60	$137.60
Purchase #5	$84.83	6.531%	$90.3702	$90.37	$90.35	$90.40
Purchase #6	$171.63	12.303%	$192.7456	$192.75	$192.75	$192.70
Purchase #7	$196.38	10.365%	$216.7348	$216.73	$216.75	$216.70
7 purchase totals =	$1,094.45		$1,190.2886	$1,190.30	$1,190.30	$1,190.20