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	$146.31	12.159%	$164.0998	$164.10	$164.10	$164.10
Purchase #2	$207.36	9.444%	$226.9431	$226.94	$226.95	$226.90
Purchase #3	$70.37	11.676%	$78.5864	$78.59	$78.60	$78.60
Purchase #4	$55.40	9.393%	$60.6037	$60.60	$60.60	$60.60
Purchase #5	$169.37	9.783%	$185.9395	$185.94	$185.95	$185.90
Purchase #6	$33.66	12.718%	$37.9409	$37.94	$37.95	$37.90
Purchase #7	$113.47	3.478%	$117.4165	$117.42	$117.40	$117.40
7 purchase totals =	$795.94		$871.5299	$871.53	$871.55	$871.40