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	$204.41	12.712%	$230.3946	$230.39	$230.40	$230.40
Purchase #2	$239.31	7.198%	$256.5355	$256.54	$256.55	$256.50
Purchase #3	$213.76	7.407%	$229.5932	$229.59	$229.60	$229.60
Purchase #4	$187.63	4.717%	$196.4805	$196.48	$196.50	$196.50
Purchase #5	$25.35	11.668%	$28.3078	$28.31	$28.30	$28.30
Purchase #6	$135.79	13.518%	$154.1461	$154.15	$154.15	$154.10
Purchase #7	$155.84	6.561%	$166.0647	$166.06	$166.05	$166.10
7 purchase totals =	$1,162.09		$1,261.5224	$1,261.52	$1,261.55	$1,261.50