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	$125.42	4.426%	$130.9711	$130.97	$130.95	$131.00
Purchase #2	$43.76	3.756%	$45.4036	$45.40	$45.40	$45.40
Purchase #3	$176.75	10.668%	$195.6057	$195.61	$195.60	$195.60
Purchase #4	$157.53	4.601%	$164.778	$164.78	$164.80	$164.80
Purchase #5	$51.99	13.600%	$59.0606	$59.06	$59.05	$59.10
Purchase #6	$210.32	9.253%	$229.7809	$229.78	$229.80	$229.80
Purchase #7	$156.40	6.783%	$167.0086	$167.01	$167.00	$167.00
7 purchase totals =	$922.17		$992.6085	$992.61	$992.60	$992.70