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	$89.92	10.381%	$99.2546	$99.25	$99.25	$99.30
Purchase #2	$55.88	6.445%	$59.4815	$59.48	$59.50	$59.50
Purchase #3	$163.87	4.264%	$170.8574	$170.86	$170.85	$170.90
Purchase #4	$124.60	5.577%	$131.5489	$131.55	$131.55	$131.50
Purchase #5	$26.31	11.763%	$29.4048	$29.40	$29.40	$29.40
Purchase #6	$237.57	13.307%	$269.1834	$269.18	$269.20	$269.20
Purchase #7	$112.69	9.543%	$123.444	$123.44	$123.45	$123.40
7 purchase totals =	$810.84		$883.1746	$883.16	$883.20	$883.20