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	$55.43	7.158%	$59.3977	$59.40	$59.40	$59.40
Purchase #2	$154.52	13.715%	$175.7124	$175.71	$175.70	$175.70
Purchase #3	$51.76	7.356%	$55.5675	$55.57	$55.55	$55.60
Purchase #4	$235.57	7.545%	$253.3438	$253.34	$253.35	$253.30
Purchase #5	$199.69	11.144%	$221.9435	$221.94	$221.95	$221.90
Purchase #6	$106.88	5.245%	$112.4859	$112.49	$112.50	$112.50
Purchase #7	$99.71	4.831%	$104.527	$104.53	$104.55	$104.50
7 purchase totals =	$903.56		$982.9778	$982.98	$983.00	$982.90