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	$30.87	5.433%	$32.5472	$32.55	$32.55	$32.50
Purchase #2	$245.41	12.697%	$276.5697	$276.57	$276.55	$276.60
Purchase #3	$233.95	9.140%	$255.333	$255.33	$255.35	$255.30
Purchase #4	$217.26	7.417%	$233.3742	$233.37	$233.35	$233.40
Purchase #5	$78.94	3.768%	$81.9145	$81.91	$81.90	$81.90
Purchase #6	$52.38	4.795%	$54.8916	$54.89	$54.90	$54.90
Purchase #7	$21.49	11.140%	$23.884	$23.88	$23.90	$23.90
7 purchase totals =	$880.30		$958.5142	$958.50	$958.50	$958.50