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	$231.99	11.434%	$258.5157	$258.52	$258.50	$258.50
Purchase #2	$42.76	6.318%	$45.4616	$45.46	$45.45	$45.50
Purchase #3	$162.73	6.853%	$173.8819	$173.88	$173.90	$173.90
Purchase #4	$16.71	9.745%	$18.3384	$18.34	$18.35	$18.30
Purchase #5	$97.28	7.694%	$104.7647	$104.76	$104.75	$104.80
Purchase #6	$166.54	13.633%	$189.2444	$189.24	$189.25	$189.20
Purchase #7	$82.34	4.166%	$85.7703	$85.77	$85.75	$85.80
7 purchase totals =	$800.35		$875.9770	$875.97	$875.95	$876.00