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	$136.40	5.689%	$144.1598	$144.16	$144.15	$144.20
Purchase #2	$39.54	4.280%	$41.2323	$41.23	$41.25	$41.20
Purchase #3	$123.86	10.181%	$136.4702	$136.47	$136.45	$136.50
Purchase #4	$212.49	8.858%	$231.3124	$231.31	$231.30	$231.30
Purchase #5	$93.76	10.437%	$103.5457	$103.55	$103.55	$103.50
Purchase #6	$23.42	8.647%	$25.4451	$25.45	$25.45	$25.40
Purchase #7	$214.38	13.363%	$243.0276	$243.03	$243.05	$243.00
7 purchase totals =	$843.85		$925.1931	$925.20	$925.20	$925.10