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	$23.53	7.783%	$25.3613	$25.36	$25.35	$25.40
Purchase #2	$100.68	11.740%	$112.4998	$112.50	$112.50	$112.50
Purchase #3	$106.72	3.609%	$110.5715	$110.57	$110.55	$110.60
Purchase #4	$243.59	4.167%	$253.7404	$253.74	$253.75	$253.70
Purchase #5	$98.80	13.291%	$111.9315	$111.93	$111.95	$111.90
Purchase #6	$21.60	13.462%	$24.5078	$24.51	$24.50	$24.50
Purchase #7	$29.94	6.705%	$31.9475	$31.95	$31.95	$31.90
7 purchase totals =	$624.86		$670.5598	$670.56	$670.55	$670.50