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	$231.72	13.830%	$263.7669	$263.77	$263.75	$263.80
Purchase #2	$135.34	9.742%	$148.5248	$148.52	$148.50	$148.50
Purchase #3	$25.81	6.780%	$27.5599	$27.56	$27.55	$27.60
Purchase #4	$49.95	10.267%	$55.0784	$55.08	$55.10	$55.10
Purchase #5	$41.34	4.615%	$43.2478	$43.25	$43.25	$43.20
Purchase #6	$98.33	7.666%	$105.868	$105.87	$105.85	$105.90
Purchase #7	$161.77	10.475%	$178.7154	$178.72	$178.70	$178.70
7 purchase totals =	$744.26		$822.7612	$822.77	$822.70	$822.80