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	$223.54	3.579%	$231.5405	$231.54	$231.55	$231.50
Purchase #2	$59.89	5.279%	$63.0516	$63.05	$63.05	$63.10
Purchase #3	$163.45	10.773%	$181.0585	$181.06	$181.05	$181.10
Purchase #4	$203.43	4.752%	$213.097	$213.10	$213.10	$213.10
Purchase #5	$131.29	5.432%	$138.4217	$138.42	$138.40	$138.40
Purchase #6	$42.38	10.681%	$46.9066	$46.91	$46.90	$46.90
Purchase #7	$19.75	10.444%	$21.8127	$21.81	$21.80	$21.80
7 purchase totals =	$843.73		$895.8886	$895.89	$895.85	$895.90