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	$45.25	13.771%	$51.4814	$51.48	$51.50	$51.50
Purchase #2	$18.56	10.470%	$20.5032	$20.50	$20.50	$20.50
Purchase #3	$35.43	11.449%	$39.4864	$39.49	$39.50	$39.50
Purchase #4	$190.88	10.742%	$211.3843	$211.38	$211.40	$211.40
Purchase #5	$103.67	8.344%	$112.3202	$112.32	$112.30	$112.30
Purchase #6	$80.33	5.256%	$84.5521	$84.55	$84.55	$84.60
Purchase #7	$144.50	12.264%	$162.2215	$162.22	$162.20	$162.20
7 purchase totals =	$618.62		$681.9491	$681.94	$681.95	$682.00