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	$15.83	5.640%	$16.7228	$16.72	$16.70	$16.70
Purchase #2	$133.99	4.180%	$139.5908	$139.59	$139.60	$139.60
Purchase #3	$182.31	3.417%	$188.5395	$188.54	$188.55	$188.50
Purchase #4	$144.68	13.731%	$164.546	$164.55	$164.55	$164.50
Purchase #5	$98.47	13.241%	$111.5084	$111.51	$111.50	$111.50
Purchase #6	$66.56	8.199%	$72.0173	$72.02	$72.00	$72.00
Purchase #7	$107.84	9.156%	$117.7138	$117.71	$117.70	$117.70
7 purchase totals =	$749.68		$810.6386	$810.64	$810.60	$810.50