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	$169.71	8.662%	$184.4103	$184.41	$184.40	$184.40
Purchase #2	$208.90	6.398%	$222.2654	$222.27	$222.25	$222.30
Purchase #3	$103.59	12.226%	$116.2549	$116.25	$116.25	$116.30
Purchase #4	$42.35	9.692%	$46.4546	$46.45	$46.45	$46.50
Purchase #5	$193.67	11.159%	$215.2816	$215.28	$215.30	$215.30
Purchase #6	$30.71	5.527%	$32.4073	$32.41	$32.40	$32.40
Purchase #7	$92.48	9.143%	$100.9354	$100.94	$100.95	$100.90
7 purchase totals =	$841.41		$918.0095	$918.01	$918.00	$918.10