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	$49.75	11.786%	$55.6135	$55.61	$55.60	$55.60
Purchase #2	$35.72	4.500%	$37.3274	$37.33	$37.35	$37.30
Purchase #3	$182.79	7.560%	$196.6089	$196.61	$196.60	$196.60
Purchase #4	$45.94	4.205%	$47.8718	$47.87	$47.85	$47.90
Purchase #5	$36.41	3.248%	$37.5926	$37.59	$37.60	$37.60
Purchase #6	$176.54	6.703%	$188.3735	$188.37	$188.35	$188.40
Purchase #7	$192.99	12.166%	$216.4692	$216.47	$216.45	$216.50
7 purchase totals =	$720.14		$779.8569	$779.85	$779.80	$779.90