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	$21.78	11.236%	$24.2272	$24.23	$24.25	$24.20
Purchase #2	$62.97	12.807%	$71.0346	$71.03	$71.05	$71.00
Purchase #3	$204.39	5.227%	$215.0735	$215.07	$215.05	$215.10
Purchase #4	$190.36	7.662%	$204.9454	$204.95	$204.95	$204.90
Purchase #5	$53.36	11.465%	$59.4777	$59.48	$59.50	$59.50
Purchase #6	$77.59	3.429%	$80.2506	$80.25	$80.25	$80.30
Purchase #7	$22.40	9.398%	$24.5052	$24.51	$24.50	$24.50
7 purchase totals =	$632.85		$679.5142	$679.52	$679.55	$679.50