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	$249.59	9.510%	$273.326	$273.33	$273.35	$273.30
Purchase #2	$164.67	13.286%	$186.5481	$186.55	$186.55	$186.50
Purchase #3	$220.41	3.254%	$227.5821	$227.58	$227.60	$227.60
Purchase #4	$54.33	3.651%	$56.3136	$56.31	$56.30	$56.30
Purchase #5	$52.54	13.337%	$59.5473	$59.55	$59.55	$59.50
Purchase #6	$183.68	4.795%	$192.4875	$192.49	$192.50	$192.50
Purchase #7	$199.95	11.854%	$223.6521	$223.65	$223.65	$223.70
7 purchase totals =	$1,125.17		$1,219.4567	$1,219.46	$1,219.50	$1,219.40