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	$233.36	8.173%	$252.4325	$252.43	$252.45	$252.40
Purchase #2	$88.52	13.602%	$100.5605	$100.56	$100.55	$100.60
Purchase #3	$40.34	7.119%	$43.2118	$43.21	$43.20	$43.20
Purchase #4	$28.88	11.229%	$32.1229	$32.12	$32.10	$32.10
Purchase #5	$85.83	12.839%	$96.8497	$96.85	$96.85	$96.80
Purchase #6	$31.59	3.547%	$32.7105	$32.71	$32.70	$32.70
Purchase #7	$217.61	4.466%	$227.3285	$227.33	$227.35	$227.30
7 purchase totals =	$726.13		$785.2164	$785.21	$785.20	$785.10