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	$104.41	6.274%	$110.9607	$110.96	$110.95	$111.00
Purchase #2	$175.29	12.692%	$197.5378	$197.54	$197.55	$197.50
Purchase #3	$81.69	11.753%	$91.291	$91.29	$91.30	$91.30
Purchase #4	$78.59	5.300%	$82.7553	$82.76	$82.75	$82.80
Purchase #5	$157.54	5.422%	$166.0818	$166.08	$166.10	$166.10
Purchase #6	$138.27	11.247%	$153.8212	$153.82	$153.80	$153.80
Purchase #7	$53.71	10.493%	$59.3458	$59.35	$59.35	$59.30
7 purchase totals =	$789.50		$861.7936	$861.80	$861.80	$861.80