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	$222.75	10.372%	$245.8536	$245.85	$245.85	$245.90
Purchase #2	$36.26	3.500%	$37.5291	$37.53	$37.55	$37.50
Purchase #3	$198.32	6.361%	$210.9351	$210.94	$210.95	$210.90
Purchase #4	$11.60	13.330%	$13.1463	$13.15	$13.15	$13.10
Purchase #5	$54.33	9.270%	$59.3664	$59.37	$59.35	$59.40
Purchase #6	$164.42	7.449%	$176.6676	$176.67	$176.65	$176.70
Purchase #7	$154.72	6.176%	$164.2755	$164.28	$164.30	$164.30
7 purchase totals =	$842.40		$907.7736	$907.79	$907.80	$907.80