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	$127.72	7.342%	$137.0972	$137.10	$137.10	$137.10
Purchase #2	$239.87	5.700%	$253.5426	$253.54	$253.55	$253.50
Purchase #3	$117.88	10.523%	$130.2845	$130.28	$130.30	$130.30
Purchase #4	$115.81	12.830%	$130.6684	$130.67	$130.65	$130.70
Purchase #5	$40.96	7.154%	$43.8903	$43.89	$43.90	$43.90
Purchase #6	$184.77	12.236%	$207.3785	$207.38	$207.40	$207.40
Purchase #7	$121.88	12.673%	$137.3259	$137.33	$137.35	$137.30
7 purchase totals =	$948.89		$1,040.1874	$1,040.19	$1,040.25	$1,040.20