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	$132.28	5.712%	$139.8358	$139.84	$139.85	$139.80
Purchase #2	$91.74	11.444%	$102.2387	$102.24	$102.25	$102.20
Purchase #3	$10.58	6.617%	$11.2801	$11.28	$11.30	$11.30
Purchase #4	$85.87	4.798%	$89.99	$89.99	$90.00	$90.00
Purchase #5	$36.93	12.192%	$41.4325	$41.43	$41.45	$41.40
Purchase #6	$84.97	4.798%	$89.0469	$89.05	$89.05	$89.00
Purchase #7	$237.54	11.356%	$264.515	$264.52	$264.50	$264.50
7 purchase totals =	$679.91		$738.3390	$738.35	$738.40	$738.20