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	$211.27	12.357%	$237.3766	$237.38	$237.40	$237.40
Purchase #2	$91.94	9.349%	$100.5355	$100.54	$100.55	$100.50
Purchase #3	$125.40	9.166%	$136.8942	$136.89	$136.90	$136.90
Purchase #4	$153.46	7.135%	$164.4094	$164.41	$164.40	$164.40
Purchase #5	$128.92	4.189%	$134.3205	$134.32	$134.30	$134.30
Purchase #6	$202.68	3.563%	$209.9015	$209.90	$209.90	$209.90
Purchase #7	$231.48	3.210%	$238.9105	$238.91	$238.90	$238.90
7 purchase totals =	$1,145.15		$1,222.3482	$1,222.35	$1,222.35	$1,222.30