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	$56.73	4.351%	$59.1983	$59.20	$59.20	$59.20
Purchase #2	$149.86	12.398%	$168.4396	$168.44	$168.45	$168.40
Purchase #3	$70.32	3.266%	$72.6167	$72.62	$72.60	$72.60
Purchase #4	$250.58	3.200%	$258.5986	$258.60	$258.60	$258.60
Purchase #5	$55.64	5.749%	$58.8387	$58.84	$58.85	$58.80
Purchase #6	$207.55	6.250%	$220.5219	$220.52	$220.50	$220.50
Purchase #7	$94.72	9.405%	$103.6284	$103.63	$103.65	$103.60
7 purchase totals =	$885.40		$941.8422	$941.85	$941.85	$941.70