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	$87.90	11.592%	$98.0894	$98.09	$98.10	$98.10
Purchase #2	$216.86	13.173%	$245.427	$245.43	$245.45	$245.40
Purchase #3	$136.33	10.579%	$150.7524	$150.75	$150.75	$150.80
Purchase #4	$74.81	5.307%	$78.7802	$78.78	$78.80	$78.80
Purchase #5	$119.56	7.601%	$128.6478	$128.65	$128.65	$128.60
Purchase #6	$228.42	8.391%	$247.5867	$247.59	$247.60	$247.60
Purchase #7	$134.38	12.402%	$151.0458	$151.05	$151.05	$151.00
7 purchase totals =	$998.26		$1,100.3293	$1,100.34	$1,100.40	$1,100.30