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	$11.64	7.293%	$12.4889	$12.49	$12.50	$12.50
Purchase #2	$199.52	4.760%	$209.0172	$209.02	$209.00	$209.00
Purchase #3	$194.81	6.782%	$208.022	$208.02	$208.00	$208.00
Purchase #4	$81.77	8.209%	$88.4825	$88.48	$88.50	$88.50
Purchase #5	$154.36	4.516%	$161.3309	$161.33	$161.35	$161.30
Purchase #6	$78.66	3.661%	$81.5397	$81.54	$81.55	$81.50
Purchase #7	$119.94	6.323%	$127.5238	$127.52	$127.50	$127.50
7 purchase totals =	$840.70		$888.4050	$888.40	$888.40	$888.30