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	$138.88	6.213%	$147.5086	$147.51	$147.50	$147.50
Purchase #2	$171.97	4.390%	$179.5195	$179.52	$179.50	$179.50
Purchase #3	$196.54	11.790%	$219.7121	$219.71	$219.70	$219.70
Purchase #4	$56.79	10.810%	$62.929	$62.93	$62.95	$62.90
Purchase #5	$60.56	11.638%	$67.608	$67.61	$67.60	$67.60
Purchase #6	$143.57	8.350%	$155.5581	$155.56	$155.55	$155.60
Purchase #7	$178.74	10.174%	$196.925	$196.93	$196.95	$196.90
7 purchase totals =	$947.05		$1,029.7603	$1,029.77	$1,029.75	$1,029.70