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	$34.85	10.107%	$38.3723	$38.37	$38.35	$38.40
Purchase #2	$118.77	9.326%	$129.8465	$129.85	$129.85	$129.80
Purchase #3	$190.52	12.723%	$214.7599	$214.76	$214.75	$214.80
Purchase #4	$95.73	7.851%	$103.2458	$103.25	$103.25	$103.20
Purchase #5	$71.40	10.159%	$78.6535	$78.65	$78.65	$78.70
Purchase #6	$192.90	4.166%	$200.9362	$200.94	$200.95	$200.90
Purchase #7	$226.31	5.503%	$238.7638	$238.76	$238.75	$238.80
7 purchase totals =	$930.48		$1,004.5780	$1,004.58	$1,004.55	$1,004.60