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	$78.56	3.622%	$81.4054	$81.41	$81.40	$81.40
Purchase #2	$109.69	4.519%	$114.6469	$114.65	$114.65	$114.60
Purchase #3	$105.50	8.481%	$114.4475	$114.45	$114.45	$114.40
Purchase #4	$95.56	4.299%	$99.6681	$99.67	$99.65	$99.70
Purchase #5	$57.72	8.351%	$62.5402	$62.54	$62.55	$62.50
Purchase #6	$245.74	6.638%	$262.0522	$262.05	$262.05	$262.10
Purchase #7	$174.85	6.806%	$186.7503	$186.75	$186.75	$186.80
7 purchase totals =	$867.62		$921.5106	$921.52	$921.50	$921.50