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	$91.56	13.687%	$104.0918	$104.09	$104.10	$104.10
Purchase #2	$136.96	13.620%	$155.614	$155.61	$155.60	$155.60
Purchase #3	$162.34	8.764%	$176.5675	$176.57	$176.55	$176.60
Purchase #4	$69.45	13.203%	$78.6195	$78.62	$78.60	$78.60
Purchase #5	$217.30	6.104%	$230.564	$230.56	$230.55	$230.60
Purchase #6	$193.34	11.395%	$215.3711	$215.37	$215.35	$215.40
Purchase #7	$229.59	7.780%	$247.4521	$247.45	$247.45	$247.50
7 purchase totals =	$1,100.54		$1,208.2800	$1,208.27	$1,208.20	$1,208.40