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	$228.36	13.281%	$258.6885	$258.69	$258.70	$258.70
Purchase #2	$158.88	9.232%	$173.5478	$173.55	$173.55	$173.50
Purchase #3	$49.46	11.331%	$55.0643	$55.06	$55.05	$55.10
Purchase #4	$11.56	12.596%	$13.0161	$13.02	$13.00	$13.00
Purchase #5	$66.69	10.257%	$73.5304	$73.53	$73.55	$73.50
Purchase #6	$106.57	4.259%	$111.1088	$111.11	$111.10	$111.10
Purchase #7	$143.60	6.452%	$152.8651	$152.87	$152.85	$152.90
7 purchase totals =	$765.12		$837.8210	$837.83	$837.80	$837.80