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	$87.78	13.692%	$99.7988	$99.80	$99.80	$99.80
Purchase #2	$28.77	9.566%	$31.5221	$31.52	$31.50	$31.50
Purchase #3	$242.94	7.558%	$261.3014	$261.30	$261.30	$261.30
Purchase #4	$63.49	8.244%	$68.7241	$68.72	$68.70	$68.70
Purchase #5	$242.48	8.192%	$262.344	$262.34	$262.35	$262.30
Purchase #6	$66.88	6.843%	$71.4566	$71.46	$71.45	$71.50
Purchase #7	$93.74	10.807%	$103.8705	$103.87	$103.85	$103.90
7 purchase totals =	$826.08		$899.0175	$899.01	$898.95	$899.00