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	$52.29	4.311%	$54.5442	$54.54	$54.55	$54.50
Purchase #2	$204.61	13.140%	$231.4958	$231.50	$231.50	$231.50
Purchase #3	$106.48	8.833%	$115.8854	$115.89	$115.90	$115.90
Purchase #4	$85.79	12.579%	$96.5815	$96.58	$96.60	$96.60
Purchase #5	$28.74	13.405%	$32.5926	$32.59	$32.60	$32.60
Purchase #6	$113.54	9.720%	$124.5761	$124.58	$124.60	$124.60
Purchase #7	$147.96	12.703%	$166.7554	$166.76	$166.75	$166.80
7 purchase totals =	$739.41		$822.4310	$822.44	$822.50	$822.50