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	$102.30	5.356%	$107.7792	$107.78	$107.80	$107.80
Purchase #2	$177.47	10.475%	$196.06	$196.06	$196.05	$196.10
Purchase #3	$39.73	7.124%	$42.5604	$42.56	$42.55	$42.60
Purchase #4	$105.51	3.768%	$109.4856	$109.49	$109.50	$109.50
Purchase #5	$187.69	3.628%	$194.4994	$194.50	$194.50	$194.50
Purchase #6	$235.54	9.789%	$258.597	$258.60	$258.60	$258.60
Purchase #7	$67.39	9.352%	$73.6923	$73.69	$73.70	$73.70
7 purchase totals =	$915.63		$982.6739	$982.68	$982.70	$982.80