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	$37.70	7.779%	$40.6327	$40.63	$40.65	$40.60
Purchase #2	$54.44	9.352%	$59.5312	$59.53	$59.55	$59.50
Purchase #3	$60.50	5.737%	$63.9709	$63.97	$63.95	$64.00
Purchase #4	$48.59	3.193%	$50.1415	$50.14	$50.15	$50.10
Purchase #5	$53.37	7.337%	$57.2858	$57.29	$57.30	$57.30
Purchase #6	$102.41	13.813%	$116.5559	$116.56	$116.55	$116.60
Purchase #7	$202.35	6.464%	$215.4299	$215.43	$215.45	$215.40
7 purchase totals =	$559.36		$603.5479	$603.55	$603.60	$603.50