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	$97.66	3.779%	$101.3506	$101.35	$101.35	$101.40
Purchase #2	$101.47	10.277%	$111.8981	$111.90	$111.90	$111.90
Purchase #3	$103.66	11.168%	$115.2367	$115.24	$115.25	$115.20
Purchase #4	$107.93	8.816%	$117.4451	$117.45	$117.45	$117.40
Purchase #5	$81.78	12.161%	$91.7253	$91.73	$91.75	$91.70
Purchase #6	$169.36	12.739%	$190.9348	$190.93	$190.95	$190.90
Purchase #7	$117.83	4.559%	$123.2019	$123.20	$123.20	$123.20
7 purchase totals =	$779.69		$851.7925	$851.80	$851.85	$851.70