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	$234.28	9.116%	$255.637	$255.64	$255.65	$255.60
Purchase #2	$68.90	4.196%	$71.791	$71.79	$71.80	$71.80
Purchase #3	$107.32	3.801%	$111.3992	$111.40	$111.40	$111.40
Purchase #4	$202.41	9.555%	$221.7503	$221.75	$221.75	$221.80
Purchase #5	$160.73	3.542%	$166.4231	$166.42	$166.40	$166.40
Purchase #6	$58.38	7.626%	$62.8321	$62.83	$62.85	$62.80
Purchase #7	$25.85	10.290%	$28.51	$28.51	$28.50	$28.50
7 purchase totals =	$857.87		$918.3427	$918.34	$918.35	$918.30