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	$48.29	6.190%	$51.2792	$51.28	$51.30	$51.30
Purchase #2	$69.76	3.366%	$72.1081	$72.11	$72.10	$72.10
Purchase #3	$70.80	9.820%	$77.7526	$77.75	$77.75	$77.80
Purchase #4	$125.57	13.559%	$142.596	$142.60	$142.60	$142.60
Purchase #5	$195.77	8.193%	$211.8094	$211.81	$211.80	$211.80
Purchase #6	$40.72	4.611%	$42.5976	$42.60	$42.60	$42.60
Purchase #7	$199.47	8.532%	$216.4888	$216.49	$216.50	$216.50
7 purchase totals =	$750.38		$814.6317	$814.64	$814.65	$814.70