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	$226.45	12.828%	$255.499	$255.50	$255.50	$255.50
Purchase #2	$172.94	13.231%	$195.8217	$195.82	$195.80	$195.80
Purchase #3	$85.63	10.840%	$94.9123	$94.91	$94.90	$94.90
Purchase #4	$28.57	8.725%	$31.0627	$31.06	$31.05	$31.10
Purchase #5	$193.61	10.690%	$214.3069	$214.31	$214.30	$214.30
Purchase #6	$247.94	9.588%	$271.7125	$271.71	$271.70	$271.70
Purchase #7	$162.82	3.351%	$168.2761	$168.28	$168.30	$168.30
7 purchase totals =	$1,117.96		$1,231.5912	$1,231.59	$1,231.55	$1,231.60