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	$25.79	10.403%	$28.4729	$28.47	$28.45	$28.50
Purchase #2	$80.69	3.176%	$83.2527	$83.25	$83.25	$83.30
Purchase #3	$25.89	11.781%	$28.9401	$28.94	$28.95	$28.90
Purchase #4	$138.49	3.295%	$143.0532	$143.05	$143.05	$143.10
Purchase #5	$79.73	3.789%	$82.751	$82.75	$82.75	$82.80
Purchase #6	$163.87	9.589%	$179.5835	$179.58	$179.60	$179.60
Purchase #7	$91.48	12.520%	$102.9333	$102.93	$102.95	$102.90
7 purchase totals =	$605.94		$648.9867	$648.97	$649.00	$649.10