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	$52.72	8.314%	$57.1031	$57.10	$57.10	$57.10
Purchase #2	$137.76	9.287%	$150.5538	$150.55	$150.55	$150.60
Purchase #3	$103.35	6.579%	$110.1494	$110.15	$110.15	$110.10
Purchase #4	$95.72	3.183%	$98.7668	$98.77	$98.75	$98.80
Purchase #5	$133.53	6.208%	$141.8195	$141.82	$141.80	$141.80
Purchase #6	$227.53	4.278%	$237.2637	$237.26	$237.25	$237.30
Purchase #7	$198.77	11.318%	$221.2668	$221.27	$221.25	$221.30
7 purchase totals =	$949.38		$1,016.9231	$1,016.92	$1,016.85	$1,017.00