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	$53.27	12.407%	$59.8792	$59.88	$59.90	$59.90
Purchase #2	$136.44	5.155%	$143.4735	$143.47	$143.45	$143.50
Purchase #3	$70.86	5.656%	$74.8678	$74.87	$74.85	$74.90
Purchase #4	$78.81	10.861%	$87.3696	$87.37	$87.35	$87.40
Purchase #5	$97.35	3.145%	$100.4117	$100.41	$100.40	$100.40
Purchase #6	$126.31	13.186%	$142.9652	$142.97	$142.95	$143.00
Purchase #7	$197.92	7.440%	$212.6452	$212.65	$212.65	$212.60
7 purchase totals =	$760.96		$821.6122	$821.62	$821.55	$821.70