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	$169.49	12.730%	$191.0661	$191.07	$191.05	$191.10
Purchase #2	$74.45	4.636%	$77.9015	$77.90	$77.90	$77.90
Purchase #3	$169.48	6.481%	$180.464	$180.46	$180.45	$180.50
Purchase #4	$206.75	4.554%	$216.1654	$216.17	$216.15	$216.20
Purchase #5	$109.42	6.789%	$116.8485	$116.85	$116.85	$116.80
Purchase #6	$51.28	5.412%	$54.0553	$54.06	$54.05	$54.10
Purchase #7	$82.28	8.624%	$89.3758	$89.38	$89.40	$89.40
7 purchase totals =	$863.15		$925.8766	$925.89	$925.85	$926.00