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	$137.91	3.665%	$142.9644	$142.96	$142.95	$143.00
Purchase #2	$47.67	10.327%	$52.5929	$52.59	$52.60	$52.60
Purchase #3	$80.29	12.786%	$90.5559	$90.56	$90.55	$90.60
Purchase #4	$97.50	9.657%	$106.9156	$106.92	$106.90	$106.90
Purchase #5	$194.83	10.681%	$215.6398	$215.64	$215.65	$215.60
Purchase #6	$97.30	11.337%	$108.3309	$108.33	$108.35	$108.30
Purchase #7	$245.40	13.747%	$279.1351	$279.14	$279.15	$279.10
7 purchase totals =	$900.90		$996.1346	$996.14	$996.15	$996.10