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	$35.90	3.855%	$37.2839	$37.28	$37.30	$37.30
Purchase #2	$116.85	6.858%	$124.8636	$124.86	$124.85	$124.90
Purchase #3	$57.34	7.372%	$61.5671	$61.57	$61.55	$61.60
Purchase #4	$74.25	10.832%	$82.2928	$82.29	$82.30	$82.30
Purchase #5	$11.36	8.257%	$12.298	$12.30	$12.30	$12.30
Purchase #6	$150.74	12.480%	$169.5524	$169.55	$169.55	$169.60
Purchase #7	$107.49	9.235%	$117.4167	$117.42	$117.40	$117.40
7 purchase totals =	$553.93		$605.2745	$605.27	$605.25	$605.40