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	$25.52	6.662%	$27.2201	$27.22	$27.20	$27.20
Purchase #2	$75.94	4.853%	$79.6254	$79.63	$79.65	$79.60
Purchase #3	$215.81	6.485%	$229.8053	$229.81	$229.80	$229.80
Purchase #4	$46.76	3.752%	$48.5144	$48.51	$48.50	$48.50
Purchase #5	$17.85	12.645%	$20.1071	$20.11	$20.10	$20.10
Purchase #6	$72.25	8.502%	$78.3927	$78.39	$78.40	$78.40
Purchase #7	$99.76	10.234%	$109.9694	$109.97	$109.95	$110.00
7 purchase totals =	$553.89		$593.6344	$593.64	$593.60	$593.60