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	$8.84	8.223%	$9.5669	$9.57	$9.55	$9.60
Purchase #2	$154.33	5.326%	$162.5496	$162.55	$162.55	$162.50
Purchase #3	$72.38	11.720%	$80.8629	$80.86	$80.85	$80.90
Purchase #4	$215.87	9.104%	$235.5228	$235.52	$235.50	$235.50
Purchase #5	$229.43	3.204%	$236.7809	$236.78	$236.80	$236.80
Purchase #6	$152.41	12.451%	$171.3866	$171.39	$171.40	$171.40
Purchase #7	$71.52	10.136%	$78.7693	$78.77	$78.75	$78.80
7 purchase totals =	$904.78		$975.4390	$975.44	$975.40	$975.50