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	$220.45	3.127%	$227.3435	$227.34	$227.35	$227.30
Purchase #2	$39.52	7.746%	$42.5812	$42.58	$42.60	$42.60
Purchase #3	$13.91	5.212%	$14.635	$14.64	$14.65	$14.60
Purchase #4	$72.70	6.601%	$77.4989	$77.50	$77.50	$77.50
Purchase #5	$186.74	6.797%	$199.4327	$199.43	$199.45	$199.40
Purchase #6	$155.56	9.157%	$169.8046	$169.80	$169.80	$169.80
Purchase #7	$160.48	4.751%	$168.1044	$168.10	$168.10	$168.10
7 purchase totals =	$849.36		$899.4003	$899.39	$899.45	$899.30