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	$42.35	6.803%	$45.2311	$45.23	$45.25	$45.20
Purchase #2	$54.55	7.403%	$58.5883	$58.59	$58.60	$58.60
Purchase #3	$21.42	7.622%	$23.0526	$23.05	$23.05	$23.10
Purchase #4	$166.37	3.333%	$171.9151	$171.92	$171.90	$171.90
Purchase #5	$151.95	4.583%	$158.9139	$158.91	$158.90	$158.90
Purchase #6	$79.83	12.778%	$90.0307	$90.03	$90.05	$90.00
Purchase #7	$247.48	8.818%	$269.3028	$269.30	$269.30	$269.30
7 purchase totals =	$763.95		$817.0345	$817.03	$817.05	$817.00