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	$53.91	9.534%	$59.0498	$59.05	$59.05	$59.00
Purchase #2	$39.82	6.466%	$42.3948	$42.39	$42.40	$42.40
Purchase #3	$159.25	7.309%	$170.8896	$170.89	$170.90	$170.90
Purchase #4	$18.52	5.675%	$19.571	$19.57	$19.55	$19.60
Purchase #5	$190.96	10.839%	$211.6582	$211.66	$211.65	$211.70
Purchase #6	$192.88	12.263%	$216.5329	$216.53	$216.55	$216.50
Purchase #7	$222.92	7.403%	$239.4228	$239.42	$239.40	$239.40
7 purchase totals =	$878.26		$959.5191	$959.51	$959.50	$959.50